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Power Supply Testing Methodology
at EXTREME Overclocking

Date Published: June 2, 2005
Author: Jason Rabel


Power supplies are a huge industry, with so many manufacturers, models, and specifications, it can become quite an intimidating task for the average consumer to choose wisely. All too often we see retail boxes with huge stickers stating the overall rated power, but exact specifications are often omitted or obfuscated. In our primer article about power supplies, we covered the basics of how a modern power supply works and many related common questions. This article is to explain how we will be testing & reporting power supplies here at EXTREME Overclocking, and hopefully allow the consumer to make better purchasing decisions.


How Much Power Does My PC Use?

Every PC consumes different amounts of power, which is why there are different sizes of power supplies available. There are devices available like the Seasonic Power Angel, or the Kill-A-Watt meter, which give reasonably accurate figures for the amount of AC power a device consumes (and can even calculate out PF automatically). If you had one of these devices, you could make a rough estimate of DC wattage requirements by guestimating your PSU is about 75% efficient. However, a more accurate method to measure the DC wattage would be to use a voltmeter & ammeter to measure each rail.

An EXTREME Overclocking Forum member has been kind enough to create & maintain a nice (and easy to use) online PSU calculator program, called the eXtreme PSU Calculator. Note: The wattage ratings that the eXtreme PSU Calculator uses are considered "absolute maximum" figures, so the total wattage calculated *should* have a reasonable amount of excess capacity compared to the actual hardware.

Determining overall power requirements is only one part of the equation, choosing a quality power supply to meet these needs is the real challenge.


Different Power Supply Specifications:

There are loads of different standards that power supplies may claim to conform to, however the three most common you will probably see is the following:

  • ATX12V (v2.2) - Maintained by Intel
  • EPS12V (v2.8) - Maintained by Intel SSI (Server System Infrastructure)
  • ATX GES - Maintained by AMD? (Pretty much defunct now, was for early MP motherboards)

While the ATX12V & EPS12V 24pin (2x12) main power connectors are pin compatible, the main ATX GES connector is different. For all practical purposes you can consider the ATX GES standard dead, there were only a couple motherboards that ever supported it. For all practical purposes any mainstream consumer level power supply will conform to the ATX12V standard, either v2.x (with split 12V rails) or the older v1.3 standard.

EPS12V specifications are a lot more beefier (with more 12V rails depending on rating) than ATX12V specs. However, some of these extra 12V rails are wired to connectors that will not fit a regular ATX motherboards (or accessories). Skim through the PDF documents for more information about this.


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