OK, I'll do it for 85 watts. That seems surprisingly low. Your computer is pretty much latest generation. I think all the circuitry now is less power hungry than just a few years back. I'm a little tired and after two cocktals I hope this is right but it seems way low, but I get 60 bucks a year at 8 cents a KW-hr. leaving it on all the time. No monitor, printer,etc. That just seems way low. Are you sure that's the load? Guess these new circuits are way more power efficient. Amazing! Why do we need a 600 watt supply if we only burn 85 watts?. In fact I had to replace a supply in one of my computers because it wasn't large enough to handle the load. Do you only need a 100 watt supply in that computer?
The PSU needs to be sized to handle the max startup/surge load. My rig doesn't have a high-end video card which can be power hungry (when they are being actively used), here are the complete specs: Asus P7P55D-E MB, Intel i7 860, 4GB DDR3 , ATI 4600 Radeon, OCZ-VERTEX 30GB SSD (Boot), WDC 1TB Drive, 3Ware 9500S RAID - 2.0TB x 3 (Seagate), 2 Optical Drives (DVD-RW), Nexus 430W PSU I checked it again, its still 85W, I ran the Windows Performance Assessment to put some active load on it and it peaked at 156W (during the CPU assessment) but went back to 85W went it was done. You should buy a Kill A Watt (http://www.p3international.com/products/special/P4400/P4400-CE.html) , you can get them for under $20 - you plug everything in and then it tells you how much power the attached devices are drawing in real-time. You can leave it attached to get the power consumption over time. Its a useful gadget.