Two GTX780 and one GTX760? Not even sure if you can even 3-SLI mismatched GPUs like that, or if including the weaker card would actually degrade fps/performance, especially within your lane limits. Or is the GTX760 a non-SLI dedicated PhysX card?
And does your system work with each of your three GPUs, one at a time? I assume that your PSU meets the minimum ATX specifications required by your mobo/proc, has enough of the right power outputs for your GPUs and other hardware, and that you've always plugged all the necessary (and optional) power feeds into your motherboard.
A 1000W PSU should suffice for your system (with two GTX780 cards), but you'd need 1200W+ with all three cards. Even more Wattage if you overclock anything. An 80Plus Silver, Gold, or Platinum PSU will have increasingly better design, build, and component qualities and be more functionally robust under load than a cheap PSU.
EVGA SuperNova, Rosewill Photons,
PC Power & Cooling FirePower Silencers are all excellent, and one or the other is on sale at newegg every week. NZXT and BeQuiet PSUs look impressive, but I've never actually tried one out. Or you could buy a somewhat expensive server-grade (or Titanium) PSU made by Seasonic, LEPA, FSP/Zalman, etc. I am of the opinion that PSUs made by Corsair, XFX, Cooler Master, and Thermaltake are often junk, regardless how much (or how little) they cost or how cool the logos or how stupidly popular the brands might be.
Warranty is a good quick-n-dirty indicator of PSU awesomeness, anything less than 5 years means cheap junk, and it's hard to beat the 10 years offered on SuperNovas (which have apparently become the favourite for the pro overclocking crowd). Buying yourself a 1600W SuperNova today would mean that you wouldn't have to buy another PSU (for one computer) for at least a full decade - it might cost a little more than other PSUs (still cheaper than Corsair, haha) but should pay for itself with overkill hassle-free reliability over the years.
"All opinions are not equal. Some are a very great deal more robust, sophisticated and well supported in logic and argument than others." - Douglas Adams
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