We measured total system power consumption at the wall socket using a watt meter. We plugged the monitor into a separate outlet, so its power draw was not part of our measurement. Also, we turned on the Athlon 64 X2's Cool'n'Quiet clock throttling function for the idle tests at the Windows desktop, but disabled CnQ for the "load" tests. In order to make sure the PPU got a good workout, we took the power draw measurements under load with the system running the Cell Factor demo in its "low" graphics setting.
Well, the PhysX card is certainly consistent. Whether it's sitting idle at the desktop or cranking away in CellFactor, it looks to add about 20 watts to the system's total power draw. That's not much in the grand scheme, and I can't help but wonder whether the PhysX card wouldn't draw more power if more fully utilized by software. The PhysX card does have an active cooling fan with variable fan speeds, and when it kicks into high gear, the fan definitely adds to overall system noise.