Editing ATX (section)

=== Efficiency ===
{{See also|Green computing|80 Plus}}

Efficiency in power supplies means the extent to which power is not wasted in converting [[electricity]] from a household supply to regulated [[direct current|DC]]. Computer power supplies vary from around 70% to over 90% efficiency.

Various initiatives exist to improve the efficiency of computer power supplies. [[Climate Savers Computing Initiative]] promotes energy saving and reduction of greenhouse gas emissions by encouraging development and use of more efficient power supplies. [[80 PLUS]] certifies a variety of efficiency levels for power supplies and encourages their use via financial incentives. Efficient power supplies also save money by wasting less power; as a result they use less electricity to power the same computer, and they emit less waste heat which results in significant energy savings on central air conditioning in the summer. The gains of using an efficient power supply are more substantial in computers that use a lot of power.

Although a power supply with a larger than needed power rating will have an extra margin of safety against overloading, such a unit is often less efficient and wastes more electricity at lower loads than a more appropriately sized unit. For example, a 900-watt power supply with the [[80 Plus Silver]] efficiency rating (which means that such a power supply is designed to be at least 85 percent efficient for loads above 180&nbsp;W) may only be 73% efficient when the load is lower than 100&nbsp;W, which is a typical idle power for a desktop computer. Thus, for a 100&nbsp;W load, losses for this supply would be 27&nbsp;W; if the same power supply was put under a 450&nbsp;W load, for which the supply's efficiency peaks at 89%, the loss would be only 56&nbsp;W despite supplying 4.5 times the useful power.<ref>{{cite web
 | url = http://www.anandtech.com/show/2624/3
 | title = Debunking Power Supply Myths
 | date = 2008-09-22 | access-date = 2014-10-07
 | author = Christoph Katzer | publisher = [[AnandTech]]
 | page = 3
}}</ref><ref>{{cite web
 | url = http://www.coolermaster.com/xresserver01-DLFILE-P130218025925ba-F13032500212140.html
 | title = Cooler Master UCP Product Sheet
 | year = 2008
 | access-date = 2014-10-11
 | publisher = [[Cooler Master]]
 | format = PDF
 | archive-date = 2014-07-28
 | archive-url = https://web.archive.org/web/20140728095533/http://www.coolermaster.com/xresserver01-DLFILE-P130218025925ba-F13032500212140.html
 | url-status = dead
 }}</ref> For a comparison, a 500-watt power supply carrying the [[80 Plus Bronze]] efficiency rating (which means that such a power supply is designed to be at least 82-percent efficient for loads above 100&nbsp;W) may provide an 84 percent efficiency for a 100&nbsp;W load, wasting only 19&nbsp;W.<ref>{{cite web
 | url = http://www.anandtech.com/show/4908/silverstone-strider-plus-500w-modular-power/4
 | title = SilverStone Strider Plus – 500&nbsp;W Modular Power
 | date = 2011-10-10 | access-date = 2014-10-11
 | author = Martin Kaffei | publisher = [[AnandTech]]
 | page = 4
}}</ref>