I've had the same tower for almost three years now. The only upgrade I have done on it is the video card. It is an ASUS Essentio CM5571 (pretty limited on what I could do to it). I did not up the PSU due to being frugal and thinking the video card requirement stating that it required a 300 watt PSU (my stock PSU happens to be 300 watts), but I did not take into account of all the other components that up the power requirements.
So, I ordered one of these, hoping this will help power all the components and give the CPU some breathing room (whenever I would run a rather demanding game, or multitask, the CPU usage will almost always be stuck high.