Software needed for measuring the power consumed by the computer

Are you serious? Why don't you just measure the AC current with an ammeter?

That's difficult to do since the duty cycle is short and the peak currents are high. The line just feeds a couple rectifiers that only cunduct when the line voltage exceeds the filter cap voltage, which may be only a few degrees of the cycle. So, you get large current pulses and lots of dead time which ampmeters don't read very well.

-Bill

Ok, then, how about a "trusty $30 Kill-A-Watt meter"?

but -

SW Technology measured a Dell Dimension 4600 at 190W using a "low-cost clamp-on ammeter"...

So have the energystar gov people got it wrong?