No, don't get that PSU. It's a no name one, so unless you do your research and can be sure that it's actually a re-branded high quality unit you risk breaking your system by using a poor quality power supply. Anyway I'd say at the least you should invest in a decent PSU like
CORSAIR Builder Series CX500 V2 $54.99http://www.newegg.com/Product/Product.aspx?Item=N82E16817139027
That should be more than enough for just about any single GPU. Again I'd say go for the GTX 460 or a Radeon 6850 (the 6850 is a little faster and uses less power) rather than the 550ti which is closer in performance to the 6770.