Hi I want to upgrade to 2 GTX 780 Ti's in SLI which each requires at least a minimum 12V current rating of 42A. Currently I'm using a Corsair GS800(v1) which features a single 12V rail with 65A. Does that then mean my GS800 won't cut it? And does amps stack meaning I would need to upgrade to a PSU with a minimum 12V current rating of 84A? Sorry if it's a dumb question but I don't really know anything about power supplies or electricity in general.