I agree that eyeballs + a calculator can go a long way. However, the amperage draw on the back of your power supply or device is typically worst-case (maximum)

I agree that eyeballs + a calculator can go a long way. However, the amperage draw on the back of your power supply or device is typically worst-case (maximum) current, not average current. Similarly, EnergyStar numbers do a little better, but everyone's usage pattern is different. For instance, what is the wattage consumed by your computer? It is certainly not the summed TDP of all components in the box. It is also not the rated wattage of your power supply. For things like this that are not "dumb loads", you need a more sophisticated way of measuring power consumption. Personally, I'm with you in preferring a different solution. I use a Kill-a-Watt (http://www.p3international.com/products/special/P4400/P4400-CE.html http://www.p3international.com/products/special/P4400/P4400-... ) to measure actual average power consumption over a few days for each major device in my home. Seems to work fairly well.