On Thu, 02 Mar 2017 09:58:26 -0500, Bob Engelhardt
wrote:

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

I had an older Pentium computer that came with a 100W PS. It worked fien
until I added more RAM and an extra Harddrive. Then it would randomly
crash or just do a reboot for no reason. Shortly afterwards, the PS just
died. I bought a 350W PS and never had another problem with that
computer. It's called RESERVE POWER. Under normal use, it only uses 54W,
but add a few drives and run it real hard, and the power use demand
rises.

This is about the same as an audio amplifier. You may have the output
tubes or transistors that will pump out 100W, but if your power supply
cant furnish the reserve power on high demand heavy bass loads, you will
hear a lot of distortion, or lose power, or worse....