How Does a Power Supply Work

How Does a Power Supply Work

If the processor can be said to be a computer’s brain, then the PSU or power supply unit is akin to its heart. It’s not much of an exaggeration to state that the power supply is the most crucial component in any PC because it keeps the rest of its components running by supplying them with a steady stream of power.

How exactly does the power supply manage to do that? If you’ve ever stopped and wondered how does a power supply work, read on to learn almost everything there is to know about it.

Getting the Right Input: How Does a Power Supply Work

Essentially, a computer power supply is a kind of sophisticated adapter. It takes the alternating current (AC) provided by your national grid and converts this into direct current (DC) used in powering the rest of the PC’s components. Different power supplies generate varying amounts of power expressed in watts (W).

The more watts they generate, the more components the power supply can service. At the back of each power supply there’s the socket known as the AC receptacle which connects it to the grid via a power cable. Right next to that is a straightforward on/off switch that cuts the power supply off from its power source when in the off position.

At the back of this receptacle there are a number of induction coils and capacitors. Their job is to “clean up” the standard AC and make it ready for use inside the PSU. Low-end models can come without these precautionary measures and are therefore prone to blowouts and other major malfunctions that can be brought on by a simple power surge that would have otherwise been easily preventable.

Next, the AC flows through a rectifier and a large transformer which convert it into high-frequency DC. Then a number of diodes convert the DC into voltages appropriate for different components. There are three main voltages or rails that the PSU can output.

The lowest one is rated at 3.3V and is used for different chipsets and DIMMS. 5V output is used for most of the motherboard’s components and some smaller motors. 12V are needed to power the larger motors located in hard disks as well as PCIe cards.

Different Types of Cables and Connectors

Each PSU has many dedicated connectors and comes with a jumble of different cables which extend out of them or can be inserted into them if the supply is modular. Since today’s computer parts all conform to certain standards, there’s little chance for error in connecting the right cable to its corresponding component.

The ATX connector is the biggest and most vital of them all. It uses 24 pins to provide an uninterrupted stream of power to the motherboard. The p4 4-pin ATX connector is a similar, smaller version of this one.

It connects the power supply to the PC’s processor. Since processors are one of the components in current systems that crave more and more power, EPS connectors are becoming a popular alternative.

SATA or serial-ATA connectors are used to power storage and DVD drives. The more of these you wish to use, the more SATA connectors your PSU should come with. They’re today’s replacement for older IDE drives which were powered by 4-pin Molex connectors. The Molex connectors are still very much alive and kicking however and are used to run fans and other devices nowadays.

Finally, there’s the 6-pin PCIe connector. It’s derived from the 4-pin variant mentioned above, and can draw more power, up to 75 watts to be exact. An 8-pin version also exists and can use twice as much. These are needed for the most advanced graphics cards that require some serious power to turn, let alone operate.


Understanding more about the internal workings of various computer parts is essential in keeping the whole system in peak working order as well as being able to diagnose and troubleshoot problems should they arise.

The power supply is a component you shouldn’t tinker with though without some prior knowledge of electrical systems. Still, with the proper knowledge you can rule it out as a potential suspect if your PC starts experiencing crashes and concentrate on other issues you might be able to fix by yourself.

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