Technology Knowledge Guide to Computer Power Supplies
Compiled by the editors at
TigerDirect.com
What is a Power Supply?
A computer power supply unit (Computer PSU) is the component that supplies
power to a computer. More specifically, a power supply is typically designed
to convert 100-120 V (North America and Japan) or 220-240 V (Europe, Asia and
Australia) AC power from the mains to usable low-voltage DC power for the
internal components of the computer. Some power supplies have a switch to change
between 230 V and 115 V. Other models have automatic sensors that switch input
voltage automatically, or are able to accept any voltage between those limits.
The most common computer power supplies are built to conform with the ATX
form factor. The most recent specification of the ATX standard is version 2.2,
released in 2004. This enables different power supplies to be interchangeable
with different components inside the computer. ATX power supplies also are
designed to turn on and off using a signal from the motherboard (PS-ON wire),
and provide support for modern functions such as the standby mode available
in many computers.
Computer power supplies are rated based on their maximum output power. Typical
power ranges are from 300 Watts to 500 Wats (lower than 300 Wats for Small form
factor systems), although units used by gamers and enthusiasts usually range
from 500 Watts to 1000 Watts, with the highest end units going up to 2 kiloWatts
for extreme performance computers with multiple processors and graphics cards
(ATI CrossFire or NVIDIA SLI).
Most computer power supplies have the appearance of a square metal box, and
have a large bundle of wires emerging from one end. Opposite the wire bundle is
the back face of the power supply, with an air vent and C14 IEC connector to
supply AC power. There may optionally be a power switch and/or a voltage selector switch.
A label on one side of the box lists technical information about the power
supply, including safety certifications maximum output wattage. Common
certification marks for safety are the UL mark, GS mark, TÜV, NEMKO, SEMKO, DEMKO,
FIMKO, CCC, CSA, VDE, GOST R and BSMI. Common certificate marks for EMI/RFI are
the CE mark, FCC and C-tick. The CE mark is required for power supplies sold in Europe.
Dimensions of an ATX power supply are 150 mm width, 86 mm height, and typically
140 mm depth, although the depth can vary from brand to brand. Before replacing
a power supply, be sure you know the capacity of the original case, so you buy
a PSU that will fit.
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