PowerMan is InWin's PSU arm. They're capable of some decent work, but what you have is a strictly low-quality budget offering. The model that your PC has is based on a rather old electrical design, ill-suited for today's 12V-hungry machines. It's surprising you had no trouble with it so far. And it is definitely not enough to even attempt to use a GTX 570. What's good, though, is that your PSU is indeed a standard ATX affair, so you don't have to go chasing an obscure form factor...
As for everyone suggesting a completely new build, there's actually some pretty sound reasoning behind it. In order for your graphics card to do any work, first the CPU has to delegate work to it. Since in modern, more demanding games, the CPU is already pretty busy with other stuff, it has little time to send work over to the GPU. This is what people mean by the GTX 570 being bottlenecked. It'll sit idly more often acceptable.
Then again, you will see some improvement, and possibly enough so that you'll be quite content with your upgrade. It's just that the 570's "talents" will be rather under-utilized. But then you can also move it to a new build later on, when you feel comfortable enough to start work on it.