BleepingComputer.com: Power Supply Function Test

Max power rating is misleading. That is the maximum wattage the PSU can put out, it is very short as it is unsustainable.

Maximum continuous power output is the rating that you want. The 1000W that your PSU is rated at is its continuous output. The efficiency is based on the power that is lost in the process. There is no 100% use of power, it will always have a loss. If the PSU puts out 1000W rated at 80% it would in reality be drawing closer to 1200W out of the wall.

RMS is a rating that is usually applied in the audio industry relating to amplification.

There is a good article that explains power ratings for PSUs, you can read it here.

This post has been edited by dc3: 24 September 2010 - 10:56 AM

Thanks, dc3

dc3, on Sep 24 2010, 11:33 AM, said:

... and this is why you suddenly (last few months) see PSUs advertised with ratings such as 80 Plus, 80 Plus Bronze, 80 Plus Silver, 80 Plus Gold, and 80 Plus Platinum. Essentially these ratings are certified by a third party and tell you how much of the power going in comes out. You can find more info here. In a nutshell, at 50% load on the PSU 80 Plus means 80% efficient, Bronze is 85%, Silver is 88%, Gold is 90%, and Platinum is 92%. The higher the rating the less power your system will pull from the wall.

Efficiency of a PSU is a subjective rating. The efficiency ratings that are listed in this article are the result of controlled conditions. This is as it should be in a scientific endeavor. The temperature is controlled, the AC power is usually brought up on a variac which produces a very precise voltage. But what happens in the real world is a little bit different.

If you will notice in that article's chart that there is a drop in efficiency at 20% and 100% pointing out that there is a sweet spot at mid range loads. The fact is that most PSU ratings are based on standby power, not 100% load ratings.

With the larger PSUs that are being used today the efficiency level goes down once it is out of a controlled environment. Part of this rating is based on room temperature, their room temperature which right at 68F. The realistic side of this is that the temperature inside the case is usually higher than the room temperature, and these larger PSUs generate more heat than the smaller ones, and this heat directly impacts the efficiency.

If you have a computer that is built for serious gaming for instance, the PSU will usually have a higher than 50% load on it. So if you are going to be realistic in choosing a PSU that will be powerful enough for your application you should look at the 100% load efficiency figure.