abhijith -
(1) You ONLY need to plug The computer, monitor, and external HHDs (ie usb devices that require external power) into the "Battery" outlet on the ups. Other devices can be powered from the "Surge protected Only" outlet, or they can be placed on a seperate Surge protector. Remember the Purpuse of an UPS is for orderly shut down, NOT to continue gaming.
(2) Your computer + monitor + USB Hard drive is Not going to require 500/550 Watts even with 2 USB Hard drives.
(a) Computer less graphics card - I would say approx 100 W (My best est not knowing your complete setup)
(b) 4850 GPU - 50 Watts Idle, 110 W gaming (double for 2 4850's)
Combined - Single GPU, Idle Approx 150 W, Gaming - approx 210 W. For two 4850's, Idle 160 - gaming Approx 320 W
(c) approx 50 W for LCD (Need to Check Data on back of your Display - And NOTE you will be less than what it says!
This yields a MAX power of about 475 W (using 75% eff for PSU)
URL for GPU power consumption
www.tomshardware.com/reviews/geforce-radeon-power,2122-6.html
(d) Cannot stress the importance of choosing a "Good" PSU
Added - good starting point:
www.tomshardware.com/forum/259002-28-will-modular-power-supply-enough. End added
Croc -
You are absolutly correct - It is the TOTAL power consummed by the devices(s) pluged in to the "Battery" protected side. WHY would you plug in a device that already has an internal battery (ie laptop with battery installed) into the "Battery" side and not the UPS output that only provides Surge protection
- And for them you could also simply plug them into a separate surge protector.
NOTE If you drew 9 Amps for more than 50 millisec, something is fried, 9 x 115 = 1035 WATTS. PSU is only ratted at 550 W. if MAXed out (Very unlikely) your input current would only be 6.4 A, assuming 75% PSU eff.