What has tentacles like a squid, a fan like a CPU, and provides all the DC electricity your computer needs? If you cheated and looked at the title of this article, then you already know I’m talking about the power supply. This metal box regulates the power influx for your desktop computer, and it’s no surprise your machine would be an inert hunk of metal without it. Electricity, after all, makes the circuits dance with activity. Let’s take a look at these electricity handlers and see just how they work.

The power supply in your computer serves the electricity to the different components of your system, like the fans, processors and drives. The power supply converts AC electricity, coursing its way through your home or office’s wiring, into low voltage DC power needed by your computer. The voltage running through most houses in the US are 100 – 120 volts. The power supply converts this high voltage to low voltage the components in the computer can use. Let’s look at the physical aspects of a common power supply before looking at the watt metrics.

An ATX Power Supply’s Appearance

A power supply unit or PSU comes mostly in standard ATX sizes. ATX refers to the size specifications of the motherboard and its related I/O connectors. The ATX power supply will fit in any ATX motherboard configuration. There are other sizes of power supplies for larger installations, like servers, as well as smaller ones for ITX motherboard constructs. The real difference between power supplies comes from the power needs of a motherboard, processor and other components.

The Power Rating

If you’ve been in the market for a power supply, you may have noticed the power rating. The power rating refers to the maximum voltage output of a particular PSU. Common PSUs will have power ratings of 300W to 500W. Certain systems require more power, like a large server, which might have a PSU with a power rating of 2kW. Smaller systems, like ITX motherboards, can utilize PSUs with as low as 150W or even smaller in some situations. The power rating can be distributed through the wired connectors coming off the power supply. These connectors output three different voltages +12v, +5v, and +3.3v. The connectors identify what type of voltage it will output. If the connector has a yellow wire, it will output +12v.  Of course these connectors are different sizes, so they cannot be interchanged easily – this prevents a casual user from inadvertently frying a component. Let’s take a look at the common PSU connectors.