I'm shopping for a UPS to run my desktop and 2 17" LCDs just long enough for me to save my work and shutdown before I lose power in the case of a power failure. I'm wondering what the typical power draw is for a system like mine. I've been looking at charts for different models of APC UPS and some say a particular model will run 10 minutes with 100W draw for example so I'm curious, how do I figure out how much power my system draws?