Hello All
  Because there has been at least 2 threads regarding power supplies and
their specs and also because the newest Computer Power User magazine has a
terrific interview with the founder of PC Power & Cooling I thought I
might pass a few tidbits on, though some of you probably already know this
stuff.  Having worked in electronics most of my life I have a healthy
respect for power supplies that work and a similarly healthy suspicion when
repairing some piece of equipment that doesn't work since it literally does
all the work.  While I know this stuff it's nice to see it put succinctly
and with real world numbers to help it make more intuitive sense.  Here
goes.

  Most manufacturers post specs that are a result of operating at 25
degrees Centigrade.  Considering there will likely be a good 15C rise just
in the PSU these specs only are good if ambient in your room is 10C which
is in the 50's fahrenheit.  Thus very often a PSU rated at 400 Watts is
really only 300 watts at real world temps, unless you've spent hundreds of
dollars on some active refrigeration, like VapoChill.  Water cooling might
help but I've yet to see one that has a water block for the PSU, though
reducing internal case temp rise would help some.

  A far more important consideration is how that wattage is divided among
the rails.  All of the hardware that consumes relatively high amounts of
current are on the +12v rail, so having massive 5v amperage ability does
little good except possibly to the manufacturer.  A further consideration
is the duration of peak power which is what handles startup unless your
machine is on 24/7.  There is no need for complicated sequential spinup if
the PSU has sufficient peak power duration.

  The last bit of which he speaks in the interview surprised me even though
I am well aware of efficiency and on-demand current draw.  Sinmply put a
larger PSU (more wattage) doesn't mean higher electric bills.  I knew that
the supply has a lower limit idle current and that it only delivers more on
demand but I didn't know anybody had greatly improved efficiency.  Dodson
claims their new 850 watt supply is so efficient ( 85% !!!) that at 10
cents a kwh it uses $65/yr (or $330 over the 5year guaranteed lifespan)
less house current than many 500 watt PSU's that are typically in the 70%
category.

  I guess the boys at PC Power & Cooling got real upset when Antec
started encroaching on their territory and decided on a roundhouse punch.

  In my experience their are other decent PSUs out there besides PC&PC
but they are correct about specmanship since few companies have stopped
using the "pie in the sky" 25C even though PC&PC has been
touting this difference for decades.  I guess most of the others figure on
consumer ignorance and in many areas it's a safe bet.  Anyway, be certain
when you are calculating your wattage needs that you pay attention to the
+12 volt rails essentially exclusively or you may end up wondering why your
system is unstable and underpowered.

 Hope this helps.

Jimmy





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