Power Supply

A power supply converts main AC to low-voltage regulated DC power for the internal components of a computer so it doesn't shorten out the system. Modern personal computers universally use a switched-mode power supply. Some power supplies have a manual selector for input voltage, while others automatically adapt to the supply 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 when the computer is powered off.

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. Recent power supplies have a standby voltage available, to allow most of the computer system to be powered off.

When the computer is powered down but the power supply is still on, it can be started remotely via Wake-on-LAN and Wake-on-ring or locally via Keyboard Power ON (KBPO) if the motherboard supports it. One thing to consider building a computer is note how much power you need for your components and buy a power supply that has more power than you need.

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