@ arges86, Probably the simplest explanation is your hardware combination with the graphics card being a major contender, required more solid power than the 500W no name brand was delivering.
If your GPU was lower quality card you may have had enough power with the old P/S, but since it requires a certain amount its own self to properly run, your system was like getting its needed power through a crimped hose, using a water hose for an example.
Now all your components have more power available than they actually need to function so they are able to draw all the power they need, and deliver to you all their capabilities they didn't have available when their power was limited.
BFG being a graphics card manufacturer knows full well the requirements necessary to power the GPU and you made a good P/S choice when you decided to go with their P/S line.
I hope that makes some kind of sense to you.