QUICK ANSWER

For modern IT equipment, routers, CCTV systems, computers, monitors, mobile devices, USB chargers and most compact electronics, an SMPS-based adaptor is generally the better technology because it is smaller, lighter, more efficient and capable of delivering relatively high power from a compact enclosure.

A traditional transformer-based/linear adaptor uses a mains-frequency transformer, rectifier and usually a regulator. It can be simple, electrically quiet and robust, but the transformer is large and heavy, and a linear regulator can dissipate substantial heat.

An SMPS (Switch Mode Power Supply) first converts the incoming AC into high-voltage DC, switches that DC at a much higher frequency, transfers energy through a high-frequency transformer or another converter topology, rectifies and filters the output, and regulates it using feedback. This allows a much smaller magnetic component and much higher efficiency.

There is no single "best" voltage, current or polarity for all adaptors. Common fixed DC outputs include 5 V, 9 V, 12 V, 15 V, 19 V and 24 V, while 48 V is also important in some networking/telecom and industrial applications. USB Power Delivery has expanded the range substantially; USB PD 3.1 defines fixed 28 V, 36 V and 48 V levels in addition to earlier levels, supporting applications up to 240 W.

For cylindrical DC barrel connectors, center-positive polarity is extremely common, but it must never be assumed without checking the equipment label, connector specification or manufacturer's documentation.

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1. COMPLETE ARTICLE

1.1 Introduction: What Is a Power Adaptor?

A power adaptor is an external power-supply unit that converts electrical power from one form into another suitable for an electronic device.

For example:

230 V AC mains → 12 V DC

or:

100–240 V AC → 5 V DC USB

The electronic equipment normally cannot be connected directly to household AC mains. Its internal circuits may require a low-voltage DC supply such as 5 V, 9 V, 12 V, 19 V or 24 V.

The adaptor therefore performs several jobs:

• Converts voltage.
• Converts AC to DC where required.
• Regulates the output voltage.
• Limits or protects against excessive current.
• Provides electrical isolation where required.
• Filters electrical noise.
• Protects both the adaptor and the connected equipment.
• Provides the appropriate connector and polarity.

Modern external power supplies are particularly important for IT and consumer electronics. IEC 62368-1:2023 specifically covers safety of audio/video and information and communication technology equipment and includes external power-supply units intended to supply equipment within its scope.

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2. Transformer-Based Adaptor vs SMPS Adaptor

The phrase "transformer-based adaptor" normally refers to a traditional mains-frequency transformer supply, often called a linear power supply.

The basic arrangement is:

AC mains → 50/60 Hz transformer → rectifier → filter → regulator → DC output

An SMPS works differently:

AC mains → EMI/protection → rectifier → high-voltage DC → high-frequency switching → high-frequency transformer/converter → rectifier → filter → regulated DC

The fundamental difference is therefore where and how voltage conversion takes place.

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3. How a Transformer-Based Power Adaptor Works

A traditional transformer adaptor can be divided into several stages.

Stage 1 — AC input

The adaptor receives mains AC, for example:

230 V AC, 50 Hz

in India.

The actual permissible input range depends on the product design and its rated specification.

Stage 2 — Mains transformer

The mains voltage is applied to a transformer.

The transformer uses electromagnetic induction to change the voltage.

For example:

230 V AC → 12 V AC

The transformer also provides galvanic isolation when appropriately designed and used.

Stage 3 — Rectification

The low-voltage AC is converted to pulsating DC.

A bridge rectifier containing four diodes is commonly used.

Conceptually:

12 V AC → bridge rectifier → pulsating DC

Stage 4 — Filtering

A large electrolytic capacitor smooths the rectified waveform.

For a full-wave rectified 50 Hz supply, the dominant ripple frequency is approximately:

100 Hz

The capacitor charges near the peaks of the waveform and discharges into the load between peaks.

Stage 5 — Regulation

The resulting DC voltage may be regulated using:

• Linear regulator
• Zener-based regulator
• Transistor regulator
• Three-terminal regulator
• More sophisticated linear regulator

For example:

16 V DC → linear regulator → 12 V DC

The unwanted voltage is largely converted into heat.

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4. How an SMPS Adaptor Works

An SMPS replaces the large 50/60 Hz transformer with a high-frequency switching system.

A simplified isolated flyback SMPS looks like:

AC mains

↓

Fuse / surge protection / EMI filter

↓

Bridge rectifier

↓

High-voltage DC

↓

Switching MOSFET

↓

High-frequency transformer

↓

Secondary rectifier

↓

Output capacitor/filter

↓

DC output

↓

Feedback circuit

↓

PWM controller

The controller continuously adjusts switching operation to maintain the required output.

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4.1 Input protection

An SMPS commonly begins with protection components such as:

• Fuse
• MOV
• NTC thermistor
• EMI filter
• X capacitor
• Common-mode choke
• Sometimes additional surge protection

Fuse

Protects against catastrophic overcurrent.

MOV

A Metal Oxide Varistor helps clamp transient overvoltage events.

NTC thermistor

Limits the initial inrush current when large input capacitors are charged.

EMI filter

Reduces conducted electromagnetic interference entering or leaving the power supply.

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5. AC-to-DC Conversion Inside an SMPS

The incoming AC is first rectified.

For a 230 V RMS sine wave, the peak voltage is approximately:

230 × 1.414 ≈ 325 V

Therefore, a conventional offline SMPS may have approximately 325 V DC peak-level bus voltage after rectification under nominal conditions, with the exact operating voltage affected by the mains range, rectifier and capacitor arrangement.

This is a critical safety point:

The primary side of an offline SMPS can contain hazardous high-voltage DC even after the AC input has been disconnected.

The bulk capacitor can retain dangerous energy.

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6. The Switching Stage

A switching transistor, usually a MOSFET in many modern designs, rapidly switches the high-voltage DC.

Instead of transforming power at 50 Hz, the transformer can operate at tens or hundreds of kilohertz depending on the topology and design.

Higher frequency allows the magnetic components to become much smaller than a 50/60 Hz transformer carrying the same power.

Common SMPS topologies include:

• Flyback
• Forward
• Half bridge
• Full bridge
• Push-pull
• LLC resonant
• Buck
• Boost
• Buck-boost
• Active-clamp flyback

For low-to-moderate-power isolated wall adaptors, flyback is particularly common.

For higher-power supplies, other topologies may provide better efficiency, thermal performance and power density.

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7. The SMPS Transformer

The SMPS transformer has several important jobs:

1. Transfers energy.
2. Provides isolation where required.
3. Changes voltage ratio.
4. Provides the appropriate secondary winding configuration.
5. Helps establish the required safety barrier between primary and secondary.

It is fundamentally different from a conventional 50/60 Hz transformer.

Because it operates at much higher frequency, its core and winding requirements are different.

Important design considerations include:

• Core material
• Core size
• Switching frequency
• Number of turns
• Primary inductance
• Leakage inductance
• Winding arrangement
• Wire size
• Insulation system
• Safety separation
• Temperature rise
• Core losses
• Copper losses

Transformer design is one of the most important parts of an isolated SMPS.

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8. Secondary-Side Rectification

After the high-frequency transformer, the secondary voltage is rectified.

Depending on output voltage and current, designers may use:

• Silicon diodes
• Schottky diodes
• Fast-recovery diodes
• Synchronous MOSFET rectification

At low output voltages and higher currents, synchronous rectification can substantially reduce conduction losses compared with a conventional diode.

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9. Output Filtering

The rectified output is filtered using combinations of:

• Electrolytic capacitors
• Ceramic capacitors
• Film capacitors
• Inductors
• Ferrite beads
• LC filters

The objective is to achieve:

• Low ripple
• Low noise
• Stable voltage
• Good transient response

The final specification may state something such as:

12 V DC, 2 A

which means the adaptor is designed to provide the specified output under its rated operating conditions.

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10. Feedback and Voltage Regulation

A regulated SMPS does not simply switch at a fixed rate and hope that the voltage remains correct.

It measures output conditions and adjusts operation.

A common isolated arrangement uses:

Output → feedback circuit → optocoupler → primary controller

The optocoupler transfers feedback information across the isolation barrier without creating a direct conductive connection between the primary and secondary circuits.

Modern controllers may use additional techniques such as:

• Primary-side regulation
• Secondary-side feedback
• Digital control
• Quasi-resonant switching
• Valley switching
• Burst mode
• Frequency reduction at light load

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11. Why SMPS Adaptors Are Smaller

This is one of the most important advantages of SMPS technology.

A 50 Hz transformer requires a relatively large magnetic core because the energy transfer occurs at a low frequency.

An SMPS transformer may operate at tens or hundreds of kilohertz.

Therefore:

Higher frequency → smaller magnetic components → smaller adaptor

This is why a modern 65 W laptop USB-C charger can be dramatically smaller than an old linear 65 W power supply.

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12. Efficiency Comparison

Efficiency is:

Efficiency (%) = Output Power / Input Power × 100

Suppose an adaptor produces:

12 V × 2 A = 24 W

If its efficiency is 90%:

Input power ≈ 24 / 0.90 = 26.7 W

Approximately 2.7 W is lost.

If another design were only 60% efficient:

Input power = 24 / 0.60 = 40 W

Approximately 16 W would be lost.

Most of that difference ultimately appears as heat.

External power supplies are subject to energy-efficiency requirements in several markets. For example, the U.S. Department of Energy maintains standards and test procedures for covered external power supplies.

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13. Which Is Better: Transformer or SMPS?

For most modern IT and electronic equipment, SMPS is the better overall technology.

However, "better" depends on the application.

SMPS is preferable when:

• Size matters.
• Weight matters.
• Efficiency matters.
• Output power is relatively high.
• Universal input is required.
• Low standby consumption is important.
• The adaptor must fit inside a compact enclosure.
• The product is a laptop, monitor, router, CCTV system, printer, charger or similar modern electronics.

Transformer/linear supply can still be attractive when:

• Extremely low electrical noise is important.
• Circuit simplicity is valued.
• Weight and size are not important.
• The power requirement is low.
• The application has unusual analogue-noise requirements.
• A very simple supply architecture is desirable.

However, a conventional linear supply is generally not the first choice for a modern compact external adaptor.

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14. Common Adaptor Output Voltages

There is no universal list that covers every electronic product, but the following voltages are widely encountered:

USB Power Delivery has significantly changed the traditional fixed-voltage landscape. USB PD 3.1 supports up to 240 W and defines 28 V, 36 V and 48 V fixed-voltage levels, alongside adjustable voltage operation.

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15. What Output Current Is Common?

Unlike voltage, current is not something the adaptor forces into the equipment.

For a conventional regulated voltage adaptor, the device draws the current it requires, provided the adaptor can supply it.

For example:

12 V 2 A adaptor

does not normally mean that 2 A is continuously forced into the equipment.

It means the adaptor is rated to supply up to 2 A at 12 V under its specified conditions.

Common ratings include:

• 5 V 0.5 A
• 5 V 1 A
• 5 V 2 A
• 5 V 3 A
• 9 V 2 A
• 12 V 1 A
• 12 V 2 A
• 12 V 3 A
• 12 V 5 A
• 19 V 2.37 A
• 19 V 3.42 A
• 19 V 4.74 A
• 24 V 1 A
• 24 V 2 A
• 24 V 5 A

These are examples of commonly encountered ratings, not a universal market-demand ranking.

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16. How to Calculate Adaptor Wattage

The basic relationship is:

Power = Voltage × Current

Therefore:

Example 1

12 V × 2 A = 24 W

Example 2

19 V × 3.42 A ≈ 65 W

Example 3

24 V × 5 A = 120 W

When designing an adaptor, the designer must consider continuous power, peak power, thermal conditions, efficiency, startup requirements and the load's transient behaviour.

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17. Adaptor Polarity

Polarity is especially important for DC barrel connectors.

The common arrangement is:

Center positive

represented approximately as:

● +

with the outer barrel connected to negative.

But center-negative also exists.

Therefore, never connect an unknown adaptor simply because the plug physically fits.

A correct replacement generally needs to match:

1. Output voltage.
2. Output current capacity.
3. Polarity.
4. Connector dimensions.
5. AC/DC type.
6. Regulation requirements.
7. Safety and compatibility requirements.

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18. Voltage Must Match

For a fixed-voltage device, the output voltage should generally match the equipment's specified input voltage.

For example:

Device requirement: 12 V DC

A 12 V regulated adaptor is the appropriate starting point.

Using a substantially higher voltage can damage the device.

Current capacity works differently.

For example:

Device: 12 V, 1.5 A

A good-quality:

12 V, 2 A

adaptor can generally be suitable because it has sufficient current capacity.

But:

12 V, 1 A

may be inadequate.

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19. Connector Size Matters

Two connectors can look almost identical but have different dimensions.

Common barrel-connector dimensions include examples such as:

• 5.5 × 2.1 mm
• 5.5 × 2.5 mm

There are many others.

A mechanically compatible connector is not necessarily electrically compatible.

For USB-C, the situation is more sophisticated because power negotiation and cable capability can affect the available power.

USB PD was specifically developed to provide negotiated and flexible power delivery rather than relying only on a single fixed voltage.

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20. Major Components of a Transformer-Based Adaptor

A basic linear adaptor can contain:

Primary side

• Mains plug
• Fuse
• Switch, where applicable
• EMI/surge components
• Mains transformer

Secondary side

• Rectifier diodes
• Electrolytic capacitor
• Voltage regulator
• Heat sink
• Output capacitor
• Indicator LED, if required
• Output connector
• Cable

For an unregulated supply, the regulator may be absent.

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21. Major Components of an SMPS Adaptor

A typical isolated offline SMPS may contain:

Input/protection

• AC plug
• Fuse
• MOV
• NTC
• EMI filter
• Common-mode choke
• X capacitor
• Y safety capacitors where appropriate

Rectification

• Bridge rectifier
• Bulk electrolytic capacitor

Switching stage

• PWM controller IC
• MOSFET
• Gate resistor/network
• Snubber or clamp components
• Current-sensing components

Magnetic section

• High-frequency transformer
• Auxiliary winding where required
• Output inductors

Secondary

• Rectifier diode or MOSFETs
• Output capacitors
• LC filtering
• Feedback circuit

Control

• Reference device
• Optocoupler in many isolated feedback architectures
• Compensation network

Protection

• Overvoltage protection
• Overcurrent/short-circuit protection
• Over-temperature protection
• Brownout/undervoltage protection
• Surge protection

Not every adaptor uses every component listed above; topology and power level determine the actual bill of materials.

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22. SMPS Manufacturing: Basic Bill of Materials

A commercial SMPS adaptor BOM typically spans several categories.

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23. Designing the Transformer

The transformer cannot simply be selected by voltage ratio.

The designer must calculate or select it based on:

• Input voltage range
• Output voltage
• Output current
• Power
• Switching frequency
• Topology
• Maximum flux density
• Core material
• Primary inductance
• Turns ratio
• Wire gauge
• Winding temperature
• Insulation system
• Creepage and clearance
• Leakage inductance
• Safety requirements

The transformer is often one of the most specialised components in an SMPS.

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24. PCB Design Is a Safety-Critical Activity

An offline SMPS PCB has a dangerous primary section and a safer low-voltage secondary section.

The PCB layout must therefore account for:

• Creepage distance
• Clearance distance
• Insulation barriers
• Slotting where appropriate
• Primary-secondary separation
• Component spacing
• Safety-rated capacitors
• Transformer construction
• PCB material
• Pollution/environment assumptions
• Thermal management

A compact PCB is not automatically a good PCB.

Reducing the board size without respecting safety distances can create a serious electrical and fire hazard.

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25. Creepage vs Clearance

These terms are often confused.

Clearance is the shortest distance through air between conductive parts.

Creepage is the shortest distance along the surface of an insulating material.

Both can be important in determining safe separation between hazardous mains circuitry and accessible low-voltage circuitry.

The exact required distances cannot safely be reduced to one universal number because they depend on the applicable standard, working voltage, insulation category, pollution degree, material characteristics, environment and construction.

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26. Safety Standards for IT Power Adaptors

For IT and AV equipment, IEC 62368-1 is now a central product-safety standard.

The current IEC publication is IEC 62368-1:2023, with a corrected version published in 2025. It uses a hazard-based approach and covers safeguards intended to reduce risks such as electric shock, injury and fire.

For India, this is particularly important because BIS/MeitY has been migrating relevant products from older standards such as IS 13252 Part 1 and IS 616 to IS/IEC 62368-1:2023. BIS currently lists power adaptors for IT equipment under IS/IEC 62368: Part 1:2023 in its Scheme-II information.

Manufacturers should therefore verify the currently applicable BIS scope, product category, certification/registration requirements and latest notifications before commercial production.

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27. EMI and EMC Requirements

A power supply is not only expected to provide the correct voltage.

It must also avoid causing unacceptable electromagnetic interference.

SMPS designs can generate:

• Switching harmonics
• Conducted noise
• Radiated noise
• Common-mode noise
• Differential-mode noise

Therefore, designers may use:

• Common-mode chokes
• X capacitors
• Y capacitors
• Ferrites
• Shielding
• Snubbers
• Optimised PCB layout
• Controlled switching edges

EMI design should be considered from the beginning, not added as an afterthought.

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28. Thermal Design

Every real power supply produces some heat.

Total losses can originate from:

• MOSFET conduction
• MOSFET switching
• Transformer copper loss
• Transformer core loss
• Diode forward loss
• Capacitor ESR
• Inductor losses
• Resistor losses
• Controller consumption

The enclosure must be designed so that components remain within their allowable temperatures.

Thermal design determines:

• Reliability
• Component lifetime
• Enclosure temperature
• Efficiency
• Maximum output power

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29. Protection Features

A modern quality adaptor may include:

OVP — Over Voltage Protection

Prevents excessive output voltage.

OCP — Over Current Protection

Limits excessive current.

SCP — Short Circuit Protection

Protects against accidental output short circuit.

OTP — Over Temperature Protection

Shuts down or limits the supply when excessive temperature is detected.

OPP — Over Power Protection

Protects the power supply when the load exceeds its designed power level.

Surge protection

Helps protect against transient input events.

These features should be designed and validated rather than simply assumed because a controller IC has a particular feature listed on its datasheet.

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30. Ripple and Noise

A DC output is not necessarily perfectly flat.

Some residual AC/switching components remain.

This is called:

Ripple and noise

For sensitive electronics, excessive ripple can cause:

• Audio noise
• Display problems
• Communication problems
• ADC errors
• Processor instability
• RF interference

A good power supply therefore requires appropriate filtering and PCB layout.

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31. No-Load and Standby Consumption

An adaptor may remain plugged into the wall even when the equipment is not operating.

Therefore, energy consumption at:

• No load
• Standby
• Light load

can be important.

Modern power-supply regulations increasingly consider these operating states. DOE's external-power-supply work, for example, explicitly addresses no-load and active-mode performance.

This is another area where modern SMPS designs generally outperform old transformer/linear supplies.

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32. Manufacturing Process for an SMPS Adaptor

A commercial manufacturing process can broadly follow these stages.

Step 1 — Electrical specification

Define:

• Input voltage
• Input frequency
• Output voltage
• Output current
• Maximum power
• Efficiency target
• Ripple/noise target
• Protection requirements
• Operating temperature
• Mechanical dimensions
• Connector
• Polarity
• Regulatory requirements

Step 2 — Select topology

Choose an appropriate architecture such as:

• Flyback
• Forward
• LLC
• Buck
• Boost
• Other appropriate topology

Step 3 — Component selection

Select:

• Controller
• MOSFET
• Transformer
• Rectifiers
• Capacitors
• Resistors
• Protection devices
• Feedback components

Step 4 — Transformer design

Develop and validate the magnetic component.

Step 5 — Schematic

Create the complete electrical design.

Step 6 — PCB layout

Separate primary and secondary sections and satisfy applicable safety constraints.

Step 7 — Prototype

Build engineering samples.

Step 8 — Electrical validation

Measure:

• Input current
• Output voltage
• Output current
• Efficiency
• Ripple
• Startup
• Shutdown
• Load regulation
• Line regulation
• Protection behaviour

Step 9 — Safety/EMC testing

Perform the applicable laboratory tests.

Step 10 — Thermal testing

Test worst-case input, load and environmental conditions.

Step 11 — Reliability testing

Potential tests include:

• Burn-in
• Temperature cycling
• Humidity
• Surge
• Short circuit
• Overload
• Drop/mechanical tests as applicable

Step 12 — Certification

Obtain the required approvals for the target markets.

Step 13 — Production

Move to controlled mass production with incoming inspection and process controls.

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33. Production-Line Testing

A serious adaptor manufacturer should not rely solely on a final visual inspection.

Typical production testing can include:

Visual inspection

Check:

• PCB assembly
• Soldering
• Component orientation
• Transformer
• Enclosure
• Cable
• Connector
• Label

Electrical safety testing

Depending on product and applicable standard:

• Dielectric strength/hipot
• Insulation resistance
• Leakage/touch current
• Ground continuity where applicable

Functional test

Verify:

• Output voltage
• Output current capability
• Startup
• Shutdown
• Protection behaviour

Load test

Test the adaptor at representative loads, including rated load where required.

No-load test

Verify standby/no-load behaviour.

Burn-in

Selected production strategies may operate units under controlled conditions for a defined period.

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34. Why Cheap SMPS Adaptors Fail

Low-quality adaptors often save money by compromising on components, design margins, thermal design, filtering, insulation or production quality.

Possible problems include:

• Undersized transformer
• Poor-quality electrolytic capacitors
• Inadequate MOSFET rating
• Weak surge protection
• Poor PCB layout
• Insufficient creepage/clearance
• Inadequate thermal margin
• Fake or low-grade components
• Poor soldering
• Insufficient EMI filtering
• Missing protection features

A low purchase price does not necessarily mean low lifetime cost.

A poorly designed adaptor can damage the equipment it powers or present an electrical/fire hazard.

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35. Why Old Transformer Adaptors Feel More "Robust"

There is a common perception that:

"Transformer adaptors are more reliable."

There is some understandable reasoning behind this.

A traditional supply can have:

• Fewer active semiconductor components
• A large, mechanically robust transformer
• Simple rectification
• Simple regulation

But reliability depends on the complete design.

An SMPS can also be extremely reliable when properly engineered.

In practice, component quality, thermal stress, electrical margins, protection design and manufacturing quality often matter more than simply whether the supply is linear or switching.

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36. Which Technology Should a Manufacturer Choose?

For a 5 V / 1 A small electronics supply

SMPS is usually the practical choice.

For a 12 V / 1–3 A router or CCTV adaptor

SMPS is generally preferable.

For a 19 V laptop adaptor

SMPS is overwhelmingly more practical because of size, weight and efficiency.

For a 65 W USB-C charger

Modern high-frequency SMPS technology is the natural choice.

For a 100–240 W USB-C PD supply

Advanced SMPS architectures are required to achieve practical size and efficiency.

USB PD 3.1 itself supports power levels up to 240 W, making modern switching architectures particularly important for high-power USB-C applications.

For an extremely noise-sensitive laboratory analogue application

A linear supply may still be useful, although hybrid architectures can also be considered.

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37. Hybrid Power Supplies

There is another important possibility:

SMPS + linear regulator

For example:

230 V AC → SMPS → 12.5 V DC → low-noise linear regulator → 12 V DC

The SMPS handles the major voltage conversion efficiently.

The linear stage then removes some residual switching noise and provides a clean final rail.

This can provide a compromise between:

• Efficiency
• Size
• Noise performance

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38. Common Mistakes When Selecting an Adaptor

Mistake 1: Matching only the connector

A connector that fits does not guarantee compatibility.

Mistake 2: Matching only voltage

Current rating and polarity matter too.

Mistake 3: Assuming higher voltage is better

It is not.

Mistake 4: Assuming a larger current rating is dangerous

For a correctly regulated fixed-voltage supply, a higher current capability is generally acceptable when the device draws only what it needs.

Mistake 5: Ignoring polarity

This can immediately damage equipment.

Mistake 6: Ignoring connector dimensions

A similar-looking barrel connector may not make reliable electrical contact.

Mistake 7: Buying only on price

The cheapest adaptor may have inadequate safety or reliability margins.

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39. Example: Selecting an Adaptor for a Router

Suppose a router label specifies:

Input: 12 V DC, 1.5 A

A suitable replacement would generally need:

• 12 V DC output
• At least 1.5 A rated output
• Correct connector
• Correct polarity
• Adequate regulation
• Appropriate safety certification

A:

12 V, 2 A

quality adaptor can generally supply the required current.

A:

9 V, 2 A

adaptor is not equivalent.

Neither is:

15 V, 2 A

simply because the current rating is adequate.

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40. Example: Laptop Adaptor

A laptop adaptor might be rated:

19 V DC, 3.42 A

Power:

19 × 3.42 ≈ 65 W

The replacement should be checked for:

• Correct voltage
• Sufficient current/power
• Correct connector
• Correct polarity
• Correct identification/communication requirements where applicable
• Appropriate safety and regulatory compliance

USB-C laptops add another layer because USB PD negotiation can determine the voltage and current actually delivered.

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41. USB-C Changes the Traditional Adaptor Model

Traditional barrel adaptors generally have a fixed output such as:

19 V DC

USB-C PD chargers can instead negotiate power.

For example, depending on charger, cable and device capability, the system can negotiate different voltage/current combinations.

USB PD 3.1 extends the fixed-voltage options to:

• 28 V
• 36 V
• 48 V

and supports up to 240 W under the specification.

This makes USB-C PD an increasingly important architecture for modern computing and consumer electronics.

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42. The Future of Power Adaptors

The trend is toward:

• Smaller size
• Higher efficiency
• Higher power density
• GaN switching devices
• SiC in appropriate higher-power applications
• USB-C PD
• Digital control
• Better thermal management
• Lower standby power
• Better EMI performance
• More intelligent power negotiation

GaN (Gallium Nitride) devices are particularly important in compact high-frequency chargers because their switching characteristics can enable higher switching frequencies and/or lower losses in suitable designs.

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43. Manufacturing Business Perspective

If the objective is to manufacture adaptors commercially, the most important decision is not simply:

"Transformer or SMPS?"

The real design question is:

What output power, voltage, current, form factor, efficiency, safety class, connector system, regulatory market and target cost does the product need to satisfy?

For example, a manufacturer may create separate product families such as:

Family A — Small DC adaptors

5 V / 1 A
5 V / 2 A
9 V / 1 A
12 V / 1 A

Family B — Networking/CCTV

12 V / 2 A
12 V / 3 A
12 V / 5 A
24 V / 2 A

Family C — Computer

19 V / 2.37 A
19 V / 3.42 A
19 V / 4.74 A

Family D — USB-C PD

20 V-class and higher-power negotiated outputs, including PD 3.1 capabilities where appropriate.

The actual product portfolio should be driven by verified customer demand rather than assuming that one voltage/current combination is universally "most demanded."

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44. Most Important Design Rule

A power adaptor should be designed as a complete safety-critical product, not simply as:

Transformer + rectifier + capacitor + connector

or:

MOSFET + transformer + controller.

The complete product includes:

Electrical design + magnetics + PCB + insulation + enclosure + thermal design + EMC + protection + cable + connector + manufacturing process + testing + certification.

That is what separates a commercial-grade adaptor from a hobby-level power supply.

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45. Final Comparison

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2) FAQ

1. Is SMPS better than a transformer adaptor?

For most modern IT and electronic equipment, yes. SMPS normally provides better efficiency, smaller size and lower weight.

2. Is a transformer adaptor safer than an SMPS?

Not automatically. Safety depends on the complete design, insulation, construction, protection and compliance testing.

3. Does an SMPS contain a transformer?

An isolated SMPS generally contains a high-frequency transformer, although not every switching converter requires transformer isolation.

4. What is the most common DC adaptor voltage?

5 V and 12 V are extremely common, while 9 V, 15 V, 19 V, 20 V and 24 V are also widely encountered depending on the equipment.

5. Is 12 V DC more common than 9 V DC?

Across many general electronics and power applications, 12 V is a very common voltage, but there is no single universal ranking applicable to every market.

6. Is center-positive polarity the most common?

Center-positive is very common for barrel-type DC adaptors, but polarity must always be verified rather than assumed.

7. Can I use a 12 V 2 A adaptor instead of a 12 V 1 A adaptor?

Generally yes, provided the voltage, polarity, connector and other electrical requirements are correct. The device normally draws the current it needs.

8. Can I use a 15 V adaptor on a 12 V device?

Generally no. Unless the equipment specifically permits that input range, the higher voltage can damage the equipment.

9. Why are SMPS adaptors so small?

They switch power at a much higher frequency than 50/60 Hz transformer supplies, allowing much smaller magnetic components.

10. Why does a transformer adaptor become hot?

Losses in the transformer, rectifier and especially a linear regulator can be dissipated as heat.

11. Why does an SMPS make electrical noise?

Rapid switching produces high-frequency electrical energy that can create conducted and radiated EMI unless properly controlled.

12. What is the purpose of an optocoupler?

In many isolated SMPS designs, it transfers feedback information across the isolation barrier while maintaining electrical isolation.

13. What does a MOV do?

A MOV helps protect the input circuit from transient overvoltage events.

14. What does an NTC thermistor do?

It can limit the high inrush current that occurs when the adaptor's bulk capacitor initially charges.

15. What is a flyback SMPS?

A flyback converter stores energy in its transformer/magnetic component during one part of the switching cycle and transfers that energy to the secondary during another part of the cycle.

16. What components are most important in an SMPS?

The controller, switching device, transformer, rectifiers, capacitors, inductors, feedback circuit and protection components are all important.

17. Can an SMPS be repaired?

Yes, but an offline SMPS contains potentially lethal voltages. Repair should be performed only by appropriately trained personnel using suitable procedures and equipment.

18. What is IEC 62368-1?

It is a product-safety standard covering audio/video and information and communication technology equipment, including relevant external power supplies.

19. Is IEC 62368-1 relevant in India?

Yes. India's regulatory framework is moving relevant IT/AV product categories toward IS/IEC 62368-1:2023, replacing older standards for applicable categories.

20. What should a manufacturer test before selling an adaptor?

At minimum, the manufacturer should establish and validate the applicable electrical, thermal, safety, EMC, reliability and production tests for the particular design and target market.

21. Is a higher current adaptor always better?

No. It is only potentially suitable if the voltage, polarity, connector and other requirements match. Current capacity by itself does not determine compatibility.

22. Is a 65 W adaptor always better than a 45 W adaptor?

Not necessarily. The equipment determines how much power it needs. A higher-rated adaptor is useful only when it is electrically compatible and the equipment can use the additional capacity.

23. What is USB PD?

USB Power Delivery is a power-negotiation technology that allows compatible devices and power supplies to negotiate suitable power levels over USB-C. USB PD 3.1 supports up to 240 W.

24. What is the future of adaptor technology?

Higher power density, GaN switching, USB-C PD, improved efficiency, lower standby consumption, digital control and better thermal/EMI performance are major trends.

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3) FINAL RECOMMENDATION / CONCLUSION

For modern IT equipment and the majority of compact electronic devices, SMPS technology is the clear practical winner.

A traditional transformer/linear adaptor still has advantages where simplicity, low switching noise and certain analogue characteristics are more important than size, weight and efficiency. But for products such as routers, CCTV systems, laptops, monitors, printers, USB chargers, networking equipment and modern consumer electronics, the advantages of SMPS are substantial.

The most important advantages are:

SMPS → smaller + lighter + more efficient + better regulated + higher power density

The most important disadvantages are:

SMPS → more complex + EMI must be controlled + design/testing are more demanding

For commercial manufacturing, the best strategy is therefore not merely to select an SMPS controller and transformer. A successful adaptor requires coordinated design of:

Input protection → EMI filter → rectifier → switching stage → transformer/magnetics → secondary rectification → filtering → feedback → protection → PCB insulation → enclosure → thermal design → EMC → safety testing → production testing → regulatory compliance.

For the Indian market, manufacturers should pay particular attention to the current BIS/MeitY regulatory framework and the migration toward IS/IEC 62368-1:2023 for applicable IT/AV products. BIS currently lists Power Adaptors for IT Equipment under the relevant IS/IEC 62368: Part 1:2023 framework.

Finally, there is no universal "best" adaptor voltage or current. A commercially successful adaptor family should be developed around verified application requirements. Common fixed-output families such as 5 V, 9 V, 12 V, 15 V, 19 V and 24 V remain important, while USB-C PD is expanding the market toward negotiated higher-power outputs, including 28 V, 36 V and 48 V under USB PD 3.1.

For anyone planning actual adaptor manufacturing, SMPS is generally the technology to invest in, particularly for compact products from roughly the low-wattage range through laptop/USB-C and other higher-power applications. The engineering priority should be safety, efficiency, thermal margin, EMI/EMC performance, component quality and regulatory compliance—not simply the lowest BOM cost.

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