On Feb 22, 7:51 am, Tomaz Cedilnik
<tcedil...@ntlworld.no.spam.please.com> wrote:
> Seems there is much more to a PSU that the wattage... What do I need to
> look for in a PSU so it will work with my machine? I've got an Athlon XP
> 2000+ (1.67 GHz).

Because so many computer assemblers do not even know how electricity
works, then power supply manufacturers have discovered how to sell a
power supply cheaper AND reap a higher profit. The naive will select
a power supply only on money and watts. Those inferior supplies leave
a glaring symptom. A long list of functions that power supplies had
to perform even 30 years ago is not provided. Those cheaper power
supplies just forget to provide those numerical specs.

Why provide those numbers when so many have no idea what those
functions are. However a decent supply can provide those facts - has
nothing to hide. These examples will also be included:
Specification compliance: ATX 2.03 & ATX12V v1.1
Acoustics noise 25.8dBA typical at 70w, 30cm
Short circuit protection on all outputs
Over voltage protection
Over power protection
100% hi-pot test
100% burn in, high temperature cycled on/off
PFC harmonics compliance: EN61000-3-2 + A1 + A2
EMI/RFI compliance: CE, CISPR22 & FCC part 15 class B
Safety compliance: VDE, TUV, D, N, S, Fi, UL, C-UL & CB
Hold up time, full load: 16ms. typical
Efficiency; 100-120VAC and full range: >65%
Dielectric withstand, input to frame/ground: 1800VAC, 1sec.
Dielectric withstand, input to output: 1800VAC, 1sec.
Ripple/noise: 1%
MTBF, full load @ 25°C amb.: >100k hrs

What happens when essential functions are missing? Short together
all power supply outputs. No damage occurs if a power supply has
those essential functions. Medium wave radio sits right next to a
computer with no interference if power supply has an essential
function. List of what is missing in cheaper supplies includes the
ability to damage motherboard and disk if an internal supply component
fails. No power supply with essential functions will damage
motherboard, et al. But then many computer assemblers have said
otherwise.

Price does not mean it is a better supply. But a very low price is
synonymous with 'missing essential functions'. No long list of
numerical specs? Then find a responsible manufacturer.

Meanwhile a supply rated at 500 watts may have same power as a more
responsible supply rated at 350 watts. They did not lie. They just
changed what was measured - leaving you to figure it out. However
watts is only a ballpark numbers - insufficient to select a supply.
You are more concerned with maximum possible current for each of 3.3,
5, and 12 volt outputs. Again, those selling only to naive computer
assemblers hope you don't learn about currents for each voltage. Good
luck hunting for responsible manufacturers. The first symptom of
inferior products - they don't want to provide that long list of
numerical specs. Otherwise you might discover missing essential
functions.