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

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.

I'll assume it's an ATX style power supply.
http://www.corsair.com/en-us/blog/2012/august/80-plus-platinum-what-does-it-mean-and-what-is-the-benefit-to-me
"Intel’s ATX specification only requires that a power supply
is 60% efficient at 50% load. Most decent quality power
supplies made in the last decade are around 70% efficient
at 50% load."

If you're getting 25%, either something is wrong, but I can't tell if
it's your measurements, a defective design, a failed power supply, or
how you're measuring the efficiency. I've made similar measurements
of an ATX power supply using a dummy load on the +5v and +12V lines,
and a Kill-a-watt meter. Typically, I obtained 75% efficiency at
about 50% of full load on a cheap ATX PS.

As MJC mentioned, the heat has to go somewhere. If your efficiency at
at 50% of maximum load (200 watts) is only 25%, then you should have
150 watts of hot air and flames coming out the back end of the PS with
the temp controlled fan spinning furiously. Something is wrong.

Photo of one of my loads:
http://802.11junk.com/jeffl/pics/drivel/slides/dummy-load-inductance.html
--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558