I didn't know diddly-squat about the make and model of server he was contemplating, and I was unwilling to waste precious minutes of my life Googling for that information -- but I told him what I do in his situation: Go get two Kill-A-Watt P4400 power meters and plug one into each power supply.
If you work in IT, or in any job that depends on electrical devices, you will eventually need something like this. I'm kind of surprised at how many IT professionals I meet who don't know that such devices exist and are inexpensive.
The Kill-A-Watt says my laptop is using 54 watts of power.
The P4400 meter is available online and at hardware stores for $20-30 US. It measures instantaneous power in watts, cumulative power in KWH, current, voltage, frequency, and power-factor. It is useful for choosing a proper size UPS and estimating runtime, figuring out what a device is costing you in electricity, finding out if dirty power is causing problems with your network gear, finding heavily loaded circuits before you start blowing breakers, and lots of other things.
It isn't the "perfect" power meter, but it gets the job done, cheap. Some of its limitations:
- Only works with standard (15-amp) plugs.
- Does not keep maximum/mimimum/peak data. (which would be really useful for measuring the start-up load of an air conditioner or refrigerator)
- No graphing or data-export function.
- Does not keep data if the power goes off.
One clever person has published a "Tweet A Watt" mod, which makes a standard Kill-A-Watt wirelessly monitorable and provides graphing and Twitter functionality. It looks like fun, but i haven't tried it yet.