newbie question on PSU

[nyker96]

So if a PSU is rated at 500W, is that the max you measure from the wall or the max DC output? So does a EA500W model max out at 500W at the wall (measured with P3 KillAWatt) or it actually is like 625W at the wall before it gets maxed?

 

[Billb2]

Actual power delivered x Efficiency = What comes out of the wall.

But a PSU rated for 500 watts likely won't be able to deliver anywhere near that power.

If you add up all the watts that it is advertised that each rail can deliver, it will add up to quite a bit more power than the power supply can provide. It's all marketing hype. "Yeah, man, I got three rails!"

Look at any spec plate on any PSU and you'll see what I mean.
For example, a PSU may be rated for 20 watts each on three 12v rails, but the total that the combined 12v rails can provide will be something like 40-50 watts.

 

[nyker96]

thanks but I mean a 500W rated PSU is for the number at wall or the DC end?

 

[HOOfan 1]

PSUs are rated for DC output...not AC input.

However different companies rate their PSUs different ways. Temperature plays a factor. Some companies rate their PSUs at 25C, others 40C others 50C and numbers in between. The higher the temperature the less DC output there will be.

Then there are those who rate at Peak power (which doesn't mean the PSU can constantly reach that output) most companies however should rate at Max continuous output. Then there are differences in output for each rail.

 

[magreen]

There's some misinformation a few posts above this one.

To answer your question simply, a psu that's rated at 500W means that the company claims it can safely put out a maximum of 500W of DC power. Which means, yes, it will draw 625W of power from the wall when delivering its max output (assuming 80% efficiency).

Whether the company's claim has any connection to reality is entirely dependent on the quality of company and their psu.

 

[Billb2]

Originally posted by: magreen
There's some misinformation a few posts above this one.

I suppose my answer was not really direct to the question, as I agree that the above PSU, if 80% efficient, would use no more than 562.5 watts from the wall outlet (450/.8).

Perhaps some clarification is required. I was just trying to point out that reading the outputs of the individual rails is folly.

Here's a typical PSU label.

Note the continuous power ratings for each of the rails:
20A x 12v = 240 watts
25A x 5v = 125 watts
12A x 12v - 144 watts
10A x 12v = 120 watts
1A x 12v = 12 watts
2A x 5v = 10 watts

That's 651 watts for a PSU rated at 450 watts????????????

And as for temperature, from reading some claims I could easily believe that some manufacturer's rate their PSU's output just before they burst into flames!