Aleksandar's computer workshop

Let's see what Aleksandar was fixing today.
My findings, tips & tricks related to computers, internet, programming and other stuff I was working with.

Why 99% of Power Supply Reviews Are Wrong

http://www.hardwaresecrets.com/article/410

http://forums.hardwaresecrets.com/why-99-power/1937
http://forums.hardwaresecrets.com/why-99-power/1937/2



1. The use of a multimeter is a declaration that the person has no idea of what they are dealing with. Multimeters sample at their designed rate and display an average which completely masks the underlying reality of wildly shifting loads. (If this were not the case, multimeters would have a blur for their least significant digits.)
2. Voltage is EVERYTHING. The current don't flow 'til the voltage says go. Current is merely the result of a voltage differential and is limited by the resistance to it.
3. The 'resistance' (readers please note the quotes before madly posting that there is more than simple dc resistance in play) presented to each rail of the PSU is a maelstrom of shifting values. One moment just a tad, at another, a gargantuan jump. It is to this nightmare that the PSU must react. Testing with static loads is a joke.
4. The specs for PSUs are NOT expressed as 'averages' - if your voltages show a sag, you're 'near the edge', if not 'in deep doodoo'! If the voltage(s) spike/sag outside the limits, ALL BETS ARE OFF.
5. PSUs are mostly 'snake oil' - sold to the indifferent and the gullible (not to mention the adamantly ignorant). I remain convinced that a 'cheap' PSU costs $2.95 to manufacture while a 'quality' unit costs $4.95; the rest is packaging, transportation, advertising and mark-up, mark-up and more mark-up.
6. The 'rating' of a PSU is pretty well WHATEVER the vendor wants it to be; they're the ones who set the parameters for the derivation. (I remember some 30-odd years ago reading an article showing how a stereo amplifier that had true specs of 5W/channel, 20-20K +/- 0.5%, THD/IMD under 1.0% could be advertised as a 200W/channel unit - LEGALLY!) The soul bragging about his 650W Q-Tec has yet to discover that it is 'rated' in peak (transient) power, not continuous (where it would be lucky to hit 425W) and that that particular brand has garnered such a bad rep that it has been abandoned.
7. PSUs are made with 'industrial' grade components (+/- 20%). The actual capacity of an assembled unit will fall in a classic bell-shaped pattern. The bean-counters are the ones who decide the 'most profitable point' between 'returns' and 'reputation'. (Anyone still believe ANTECs are 'built like tanks'? There was a time...)
8. The 'average' system draws less than 200W from the wall socket. Those who cannot grasp the difference between 'average' at the wall and instantaneous 'peak' (all rails SIMULTANEOUSLY) at the PSU output will continue to live on their 'luck of the draw', convinced that a 450W unit can run anything.
I doubt I will ever see a PSU evaluation that actually 'tests' the PSU's ability to maintain voltages within spec (down to the microsecond, or at least millisecond) while each rail was being jumped (both up and down) by 1,2,3...max amps from each possible point (1, 2, 3...max amps), SIMULTANEOUSLY at RANDOM rates. But then, I doubt there is a PSU that could pass.
And considering that component manufacturers are no more forthcoming in their actual peak demands, it probably doesn't matter.
Caveat emptor.