You will want a new PSU. Dynex is iffy.
I have this one, could run a 550ti no problem:
http://www.newegg.com/Product/Product.aspx?Item=N82E16817371029 Antec is one of the best around.
Its bigger brother has 2 PEG power connectors for GPU's in case you ever want to upgrade to a more powerful GPU:
http://www.newegg.com/Product/Product.aspx?Item=N82E16817371030
And if you buy like today, get their even bigger brother, on sale for $30 off!
http://www.newegg.com/Product/Product.aspx?Item=N82E16817371031
Now that my Antec fanboyism is done, I'll give you a more objective suggestion and that is that any unit from Antec, Seasonic, XFX, and Corsair would work just fine. Those are the best PSU brands.