Computer Power Supply

Everything you need to know about a computer's power supply unit

Corsair Enthusiast TX650 V2 ATX12V EPS12V Power Supply


The power supply unit is the piece of hardware that converts the power provided from the outlet into usable power for the many parts inside the computer case.

It converts the alternating current from your wall outlet into a continuous form of power called direct current that the computer components require. It also regulates overheating by controlling voltage, which might change automatically or manually depending on the power supply.

The power supply is a crucial piece because, without it, the rest of the internal hardware can't function. Motherboards, cases, and power supplies all come in different sizes called form factors. All three must be compatible to work properly together.

CoolMax, CORSAIR, and Ultra are the most popular PSU makers but most are included with a computer purchase, so you only deal manufacturers when you replace the PSU.

A PSU is not usually user serviceable. For your safety, never open a power supply unit.

Power Supply Unit Description

Photo of a Corsair Enthusiast TX650 V2 ATX12V EPS12V Power Supply
Corsair Enthusiast TX650 V2 ATX12V EPS12V Power Supply. © Corsair

The power supply unit is mounted just inside the back of the case. If you follow the computer's power cable, you'll find that it attaches to the back of the power supply. It's the backside that's usually the only portion of the power supply that most people will ever see.

There's also a fan opening at the back of the power supply that sends air out the back of the computer case.

The side of the PSU facing outside the case has a male, three-pronged port that a power cable, connected to a power source, plugs into. There's also often a power switch and a power supply voltage switch.

Large bundles of colored wires extend from the opposite side of the power supply unit into the computer. Connectors at the opposite ends of the wires connect to various components inside the computer to supply them with power. Some are specifically designed to plug into the motherboard while others have connectors that fit into fans, floppy drives, hard drives, optical drives, and even some high-powered video cards.

Power supply units are rated by wattage to show how much power they can provide to the computer. Since each computer part requires a certain amount of power to function properly, it's important to have a PSU that can provide the right amount. The very handy Cooler Master Supply Calculator tool can help you determine how much you need.

More Information on Power Supply Units

Photo of a Sentey Bxp450-ps Power Supply
Sentey Inc.

The power supply units described above are the ones that are inside a desktop computer. The other type is an external power supply.

For example, some gaming consoles have a power supply attached to the power cable that must sit between the console and the wall. Others are similar, like the power supply unit built-in to some ​external hard drives, which are required if the device can't draw enough power from the computer over USB.

External power supplies are beneficial because it allows the device to be smaller and more attractive. However, some of these types of power supply units are attached to the power cable and, since they're generally pretty large, sometimes make it difficult to position the device against the wall.

Power supply units are often victims of power surges and power spikes because it's where the device receives electrical power. Therefore, plug the device into a UPS or surge protector.