The GTX 550Ti's max power draw is only 116W, and assuming you have a power hungry 125W CPU, that's only 241W. Including your mobo, RAM, HDDs, SSDs, DVD drive and Misc, you can't go over 500W in the most power hungry scenarios, which leaves you with at least 100W for future additions (i.e HDDs, SSDs, etc). My answer is yes, it will power your whole system with room to spare.
GTX 560Ti power draw source via link below.
http://www.gpureview.com/geforce-gtx-550-ti-card-647.html
@Dirtyferret I doubt the Ultra 600W PSU is a real life 450W PSU because I ran a Phenom II x4 945 and two XFX 5770 in xfire on a 600W Ultra PSU for at least a year before I made a new rig. Please don't insult non-main stream brands out of the blue, it saddens me.
~Coffee