A power supply unit (or PSU) converts mains AC to low-voltage regulated DC power for the internal components of a computer. Modern personal computers universally use switched-mode power supplies. Some power supplies have a manual switch for selecting input voltage, while others automatically adapt to the mains voltage.
Most modern desktop personal computer power supplies conform to the ATX specification, which includes form factor and voltage tolerances. While an ATX power supply is connected to the mains supply, it always provides a 5 Volt standby (5VSB) voltage so that the standby functions on the computer and certain peripherals are powered. ATX power supplies are turned on and off by a signal from the motherboard. They also provide a signal to the motherboard to indicate when the DC voltages are in spec, so that the computer is able to safely power up and boot. The most recent ATX PSU standard is version 2.31 as of mid-2008.
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.
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.
The fan inside a power supply should always be running. If the fan is not running ,either the computer is not working or the fan inside the power supply has failed and the power supply should be replaced.
The best power supply for your PC build is the one that provides the right amount of wattage to all components simultaneously. Manually calculating this requires that you multiply the total amps of all components by the total volts of all components. The result is the total watts that your PC build requires. If you input all the components of your PC build into our calculator, it will do this for you and provide a list of options.
Every PC case has a space for the power supply unit although the space may vary in size and shape. For example, small form factor cases will not be able to accommodate a PSU meant for a mid or full tower case. It is always best to look at the dimensions of your PC case and make sure that you are buying a power supply unit that can fit in the designated space.
Many power supplies have an external switch located at the rear of the unit. Check that it has not been accidentally been switched off. Plug the PSU power cable into a wall socket or surge protector, and turn on the computer. Most power supply models have a light on back of the unit that glows when it’s powered on. If it doesn’t light, try a different power cable and a different socket to eliminate those items as the source of the problem.
No, power supplies output whatever the system load is. For example, A 1200W PSU will still only output 300W if that is what the system demands from it. Only power supply energy efficiency differences will affect your electricity costs.