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MJC

In article ,
says...

I have an old PC that recently lost its PS. An identical one was hard
to find, but I didn't know the PC's power requirements, so I couldn't
use a generic PS. I should say that I thought I couldn't use a generic one.

I measured the PC's power use so next time I'll be ready. It was quite
surprising - the PS is "400W", but the PC only uses 54W. And there's
40A of 5V available, but only 5A are used. Etc.

The biggest surprise was the PS's efficiency, or lack thereof. A
Kill-a-watt on the input showed 200w being used, and 54w output. 25%
more or less. I thought that a SMPS would be way more efficient than that.

Bob

The energy has to go somewhere. If your measurement is to be trusted
(real RMS?) then the PSU fan must be working like a hairdryer!

And what do you mean "lost its PS"? It vanished in a puff of smoke,
leaving not even a specification plate behind?

Mike.