That system should run fine with a 450W PSU. The 7750 does not require a power connector so no need for that. What brands is it, as asked above. If it's an el-cheapo everyone is going to tell you to replace it.
The hyber TX-3 should be fine. The cooler itself is not wider than the socket, just the fan hands over so it shouldn't stick out far enough to be concerned about tall RAM. if it was a wider cooler you may have to reconsider.
thanks mate, you wanna say Hyper TX3 will fit with tall ram on my mobo!!