Power Supply Requirements

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Postby Rabidwerewolf » Sun Jul 01, 2007 9:16 pm

I've read through this sticky, and I would like to add one piece of advice that I have not seen mentioned. In figuring out how much wattage you need and therefore, what power supply you will be getting, it is very important to take into consideration that no power supply is 100% efficient. In other words, there will always be some loss when converting AC to DC due to the inefficiency of electrical devices. In addition you also need to take into consideration the effect of power output and consumption as capacitors age. Older capacitors equals less efficiency.

Don't always take the efficiency rating that the actual power supply company slaps on its product. It is usually not an average, but the best rating one power supply may have gotten out of "xx" number, and/or it may not be the efficiency rating at peak output. It is wiser to go by independent third party reviews and lab tests. One good site to get efficiency ratings is:


Just click on the computer industry tab followed by the view certified products and suppliers to get to this list of power supplies with an average efficiency rating of at least 80% or higher:


When testing or looking at reviews of power supplies, the volt-amp value(which is known as VA) is how much power is being consumed by the power supply being tested to provide the wattage value. The higher the VA value is, the more electricity is being used by the power supply, and the less efficient it is. The closer the volt-amps and wattage figures are to each other, the more efficient a power supply is. This is called the Power Factor(PF): wattage / volt-amps = PF. Power supplies generally are anywhere from 70% efficient as far as the poorer quality ones go, 75% to 80% for average quality, at least 80% to 83% for good quality, to as high as 85% to 88% for very high quality power supplies. Based on this, whatever wattage power supply you take a look at getting, you need to take that power supplies efficiency rating into account. In other words, if you can not find an efficiency rating on a power supply other than what the manufacturer supplies, I would not recommend getting it no matter how good the brand name.

Here is another good site:


This is a good site if you don't know the actual manufacturer of your PSU as it explains how to find out:


I hope this info provides useful in making your next decision to purchase your next power supply.
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Postby mr newbie » Sun Feb 15, 2009 10:42 pm

Ryn wrote:just found this one and i think its a good psu calculator, it even calculates your oc'ed rigs :wink:

eXtreme PSU Calculator

I like this one, pretty detailed. Take it with a grain of salt though, as OC'ing one cpu on there actually dropped the total wattage estimate...... :lol:
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