Abbreviated as PS or P/S, a power supply or PSU (power supply unit) is a hardware component of a computer that supplies all other components with power. The power supply converts a 110-115 or 220-230 volt AC (alternating current) into a steady low-voltage DC (direct current) usable by the computer and rated by the number of watts it generates. The image to the right shows an Antec True 330, a 330 Watt power supply.
Never open the casing of a power supply. It contains capacitors capable of holding a strong electrical charge, even if the computer is off and unplugged for an extended period.
You can protect your power supply and your computer from surges and voltage drops by investing in a UPS. If you cannot afford a UPS, you should at the very least have the computer plugged into a surge protector.
Where is the power supply located in a computer?
The power supply is located at the back of the computer, usually at the top. However, many more recent tower computer cases house the power supply at the bottom., the power supply is usually located at the top back or bottom back of the case. In a desktop computer case (all-in-one), the power supply is located at the back left or back right.
Parts found on the back of a power supply
Below is a list of parts you may find on the back of the power supply.
- A connection for the power cord to the computer.
- A fan opening to heat out of the power supply.
- A red switch to change the power supply voltage.
- A rocker switch to turn the power supply on and off.
On the front of the power supply, which is not visible unless the computer is opened, you will find several cables. These cables connect to the computer motherboard and other internal components. A power supply connects to the motherboard using an ATX style connector and may have one or more of the following cables to connect power to other devices.
Parts found inside a power supply
Below is a list of parts you will find inside a power supply.
- A rectifier that converts AC (alternating current) into DC.
- A filter that smooths out the DC (direct current) coming from a rectifier.
- A transformer that controls the incoming voltage by stepping it up or down.
- A voltage regulator that controls the DC output, allowing the correct amount of power, volts or watts, to be supplied to the computer hardware.
The order in which these internal power supply components function is as follows.
- Voltage Regulator
What items are powered by the computer PSU?
Everything contained in the computer chassis is powered by the power supply. For example, the motherboard, RAM, CPU, hard drive, disc drives, and most video cards (if the computer has one) are all drawing power from the power supply. Any other external devices and peripherals, such as the computer monitor and printer, have their own power source.
Does the fan always run on a power supply?
While the computer is on the fan(s) inside a power supply should always be running. If the fan is not running (spinning), either the computer is not working or the fan inside the power supply has failed and the power supply should be replaced.
Some power supplies have variable controls that may increase or decrease the speed of the fan depending on its temperature. However, it should always be spinning.