UK How an AC adapter works
An AC adapter is a power supply that sits outside the device it powers. It takes alternating current (AC) from a mains socket and turns it into the steady, low-voltage direct current (DC) that electronics run on. Laptops, mini PCs, monitors, routers and many panel PCs use one instead of a power supply built into the case.
Strictly it is an AC-DC adapter, because the output is DC. Nearly all current adapters are switch-mode designs: they rectify the mains, switch it at high frequency through a small transformer, then regulate and filter the output. That is why a 65 W laptop adapter fits in a hand, where an old linear adapter of the same rating would have been several times heavier.
Most adapters accept a universal input of 100 to 240 V at 50 or 60 Hz, so the same one works in the UK, Europe and North America with only a different mains lead or plug. People also call the larger inline type a power brick, and the type that plugs straight into the socket a wall adapter.
Types of AC adapter
Adapters differ in shape, connector and how the output is set. The type decides how securely the power stays connected and which devices it can serve.
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Wall-plug adapter. The supply is built into the plug. Common for routers, small displays and low-power devices up to around 30 W.
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Desktop or inline adapter. A separate brick with a mains lead on one side and a DC lead on the other. Used for laptops, mini PCs, monitors and panel PCs, usually from 36 W to around 200 W.
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USB-C Power Delivery adapter. The device negotiates the voltage over the cable. USB Power Delivery, defined by the USB-IF, reaches 100 W, and up to 240 W with the Extended Power Range in revision 3.1.
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Medical-grade adapter. Built to IEC 60601-1, with lower leakage current and stronger isolation, for equipment used near patients.
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Locking-connector adapter. Uses a screw-lock or latching DC plug, or a terminal block lead, so the power cannot be knocked out on a machine or cart.
How to read an AC adapter label
Every adapter carries a rating label, and almost every compatibility question can be answered from it. Compare it with the input marked on the device, usually beside the DC socket.
| Label field | Typical marking | What to check |
|---|---|---|
| Input | 100–240 V ~ 50/60 Hz 1.5 A | Universal input works worldwide; the current is the most it draws from the mains |
| Output voltage | 12 V ⎓ | Must match the device exactly; ⎓ means DC |
| Output current | 5 A (60 W) | Equal to or higher than the device needs; the device only draws what it uses |
| Polarity | Centre-positive symbol | Must match; centre-positive is the most common |
| Connector | 5.5 × 2.5 mm barrel, or USB-C | 5.5 × 2.1 mm and 5.5 × 2.5 mm look alike but fit loosely if mixed |
| Efficiency level | VI | Level VI meets the US DoE rule; EU sales follow Regulation (EU) 2019/1782 |
| Safety marks | CE, UKCA, UL, IEC 62368-1 | Shows the adapter was assessed to the current IT equipment safety standard |
The voltage and polarity are the two values that can damage a device if they are wrong. A higher current rating than needed is safe, while a lower one makes the adapter run hot, shut down or reset the device under load.
AC adapter vs power supply
An AC adapter is a power supply; it is just the external kind. A desktop PC has its supply inside the case, producing several DC rails at once. A device with an adapter receives a single DC voltage and converts it again on its own board into the lower voltages the processor, memory and storage need. Our guide to what a computer power supply does covers internal, redundant and DC-input supplies in more detail.
Putting the supply outside the device has trade-offs. It keeps heat and mains voltage out of a small or fanless enclosure and makes a failed supply quick to replace, but it adds a second box and a cable joint that can be pulled loose. For permanent installations, a mains supply in the cabinet, such as one of our industrial power supplies, is often the tidier answer.
How industrial computers are powered
Industrial and embedded computers take power in two main ways, and the choice depends on what is available where the system is installed.
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12 V DC with an AC adapter. Many of our panel PCs and industrial monitors run on 12 V DC and are supplied with a 100 to 240 V AC adapter for use in offices, control rooms and indoor cabinets.
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Wide-range DC input. Many box PCs, DIN-rail PCs and in-vehicle computers accept a wide-range input, such as 9 to 36 V DC, on a terminal block. They run straight from a 12 V or 24 V cabinet supply or a vehicle battery, with no adapter at all.
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Backup power. Where a clean shutdown matters, an industrial UPS with supercapacitor storage sits between the supply and the computer and rides through short dropouts.
Quick answers on AC adapters
AC adapters: common questions
What does an AC adapter do?
It converts mains power for a device. It turns 100 to 240 V AC from the socket into the single low-voltage DC supply the device is designed for, and protects against over-current and short circuits.
Is an AC adapter the same as a charger?
Often, but not always. A laptop adapter is usually called a charger because the laptop uses it to charge its battery. A device without a battery, such as a monitor or mini PC, uses the adapter purely as its power supply.
Can I use a different AC adapter?
Yes, if it matches. The voltage, polarity and connector must be the same, and the current rating must be equal or higher. A different voltage or reversed polarity can damage the device.
Why does my AC adapter get hot?
Some warmth is normal. No conversion is perfectly efficient, and the lost energy becomes heat. An adapter that is too hot to hold, smells or clicks may be undersized or failing and should be replaced.
What does an AC adapter look like?
Usually a plug or a small box on a cable. Wall adapters are a thick plug with a DC lead. Desktop adapters are a rectangular brick with a mains lead on one side and a DC lead on the other.
We specify the power input for every system we build, supply the matching AC adapter, cabinet supply or UPS, and validate it with the computer as standard before it ships. Tell us what power is available on site, and we will match the supply to it.