I'm looking to get a second 560 ti ( Gigabyte GeForce GTX 560 Ti Overclocked 1GB ) and run it in SLI with my MSI GeForce GTX 560 Ti Hawk 1GB. I have a Thermaltake 700w Litepower PSU, so will it be enough to run my two cards?
Lets say 42A. 42A * 12V = 504W. Let's assume you have a 95W CPU and take away 50W more for the board, drivees, etc and that leaves you with around 350W for your GPUs. The TDP of the 560TI is officially 170W, so 340W is needed for SLI.
So yes, technically you have enough power. What delluser didn't say in that power however that 65% efficient PSUs, and those that don't clearly state how much power is on the 12V rail shouldn't be used. Period. More so if this is a many years old PSU that you've been carrying over from build to build. Retire it, get a new one. If it did work, it won't for long.
700w is cutting it to short for comfort and wouldn't do it my self. At stock they run 160-180w each and fully overclocked a typical 950mhz to 1ghz gtx 560ti run about the same power consumption as a single gtx 570. Around 225w each so I suggest a more powerful unit or not overclock. At stock they should not be a issue but have to factor in the needs of the rest of the system.
Why would you spend more money on overclocked cards to then underclock them because of your PSU? What happens when down the road you want to upgrade and then you are stuck with a PSU that won't cut it, so you will have to spend the cost of a gpu AND a new psu all at once?
You said you JUST got the psu.. well return it.. use the money plus a little bit more to buy another, more effecient one.
Also - underclocking them will only lower the power consumption slightly. Not enough to make a real difference.