Thank you for all your replies.
I was told that my Antec TruePower New 650watt would be plenty enough to run 2 GTX 560 ti in SLI.
I used PSU Calculator v0.98. It told me a 550watt would be enough power. http://www.overclock.net/power-suppl...a-release.html
My PSU has 54A total. Which according to MSI 2 GTX 560ti SLI only requires 42A. http://forum-en.msi.com/faq/article/...graphics-cards