Power supply unit (computer)
The top cover has been removed to show the
internals of a computer Power supply unit.
This article is about the common off-line
switching power supplies used in
desktop IBM PC compatible computers.
There are many other kinds of computers
with differing power supplies.
A power supply unit (PSU) is the compon-
ent that supplies power to a computer. More
specifically, a power supply is typically de-
signed to convert 100-120 V (North America
and Japan) or 220-240 V (New Zealand,
Europe, South America, Africa, Asia and Aus-
tralia) AC power from the mains to usable
low-voltage DC power for the internal com-
ponents of the computer. Some power sup-
plies have a switch to change between 230 V
and 115 V. Other models have automatic
sensors that switch input voltage automatic-
ally, or are able to accept any voltage
between those limits.
The most common computer power sup-
plies are built to conform with the ATX form
factor. This enables different power supplies
to be interchangeable with different compon-
ents inside the computer. ATX power sup-
plies also are designed to turn on and off us-
ing a signal from the motherboard, and
provide support for modern functions such as
the standby mode available in many com-
puters. The most recent specification of the
ATX standard PSU as of mid-2008 is version
2.31.
Power rating
Computer power supplies are rated based on
their maximum output power. Typical power
ranges are from 300 W to 500 W (lower than
300 W for Small form factor systems) and are
intended for ordinary home computers, the
use of which is limited to Internet-surfing and
burning and playing DVDs. Power supplies
used by gamers and enthusiasts mostly range
from 450 W to 1400 W. Typical gaming PCs
feature power supplies
in the range of
500-800 W, with higher-end PCs demanding
800-1400 W supplies. The highest-end units
are up to 2 kW strong and are intended
mainly for servers and, to a lesser degree, ex-
treme performance computers with multiple
processors, several hard disks and multiple
g