I wanted to see how much my whole computer was pulling including my monitor, so I bought a "Kill A Watt" meter. Basically you plug you pug in it and it into the wall.
Kill A Watt
So what I did was plug everything into a power strip and plug the strip into it.
This is what I was running off of it..... My 20" monitor, my Antec 550 PSU, my second PSU... those two were running...... two water pumps, 1 245w Peltier, 2 DVD RW, three hard drives, MB & CPU (obviously).....3 120mm fans, 6 80mm fans... a fan regulator, 2 12" cathodes and a crap PCIe video card.
Wanna know how much all that was ACTUALLY pulling....
I am definitely a believer that you do not need a PSU with enough power to run a small town... just a quality one!