[geeks] New Intel Atom-based barebones system

[der Mouse]

>> What sort of power factor (ball park) do computer power supplies have?

> Well, Antec makes a big deal about their new, power-efficient, 80+
> percent efficient power supplies, so I infer that "normal" power
> supplies are less than 80% efficient (that means the power supply
> takes 100 watts from the wall to produce 80 watts, correct?).

That's what I would interpret efficiency as.

But that's got very little to do with the power factor.  The power
factor is the ratio between RMS volts time RMS amps and actual power
consumed (the latter being the integral of the product of instantaneous
volts and instantaneous amps).

A simple resistor, for example, has power factor 1; voltage and current
are always exactly in phase.  An ideal inductor or capacitor will draw
current, but it will be 90 degrees out of phase with the voltage, so
the actual power drawn will be zero and the power factor will also be
zero.

SMPSUs are more complicated, because they do not draw a sine wave of
current - draw zero current except nera the peaks of the voltage
sinewave.  I'd have to do more math than my brain is up to at this hour
to work out their power factor.  (You might think linear supplies would
work the same way, and to an extent they projbably do - but, if they
have transformer input stages, the energy storage in the transformer's
magnetic field acts to smooth things out substantially.)

This has almost nothing to do with the ratio of power going into a
power supply to power coming out, which is its efficiency.

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