I'm no expert but it's probably a good place to start. I run mine from a 650w one (older, with new batteries), with a 750w power supply. My components use 414w (est.) plus my two monitors and my router/modem. I have tested it and it all ran for about 3 minutes just fine on battery with 3dmark running at which point I shut it down and plugged the UPS back into the mains. I never leave my rig running unattended so this is all I need.