Some good points, above, a little confusion.
1) That 500W power supply looks adequate. In your case it was the Amp's (current) supplying the graphics card you're getting that's important. The basic specs look okay at first glance. *NOTE that an older PSU can always fail under a larger load even if it's specs say it should be fine.
2) NEW PSU:
Again, if you intend to SLI or Crossfire you need to pay special attention to the Amp's available. Basically you want to get between 850W and 1000W for something like 2x570.
You should spend some time reading, but glancing at a great online store, NCIX here's some quick recommends:
http://www.ncix.com/products/?sku=45896&vpn=RS-A00-AMBA-J3&manufacture=COOLERMASTER
http://www.ncix.com/products/?sku=58862&vpn=OCZ-ZX1000W&manufacture=OCZ%20Technology
http://www.ncix.com/products/?sku=47753&vpn=ST1000-P&manufacture=Silverstone%20Technology
http://www.ncix.com/products/?sku=57846&vpn=PPCS910&manufacture=PC%20Power%20%26%20Cooling
http://www.ncix.com/products/?sku=53719&vpn=CMPSU-850AX%20A&manufacture=Corsair
http://www.ncix.com/products/?sku=47587&vpn=CP-1000&manufacture=Antec#CustomerReviews
OTHER POINTS:
1) There's a small window of opportunity to add a second card, after which the card disappears or becomes too expensive (sometimes only six months).
2) most people find they either get SLI/Crossfire right away or else they end up waiting and replacing the current card in two to four years
3) 2xGTX 570 in my opinion is a waste of money. Most games can run at maximum quality at 60FPS with a GTX 560Ti.
4) If you wish to spend the money and want NVidia, I strongly recommend getting a 2x560Ti setup.
5) carefully measure your power supply and graphics card to make sure they fit your case.
6) The graphics card in a well-designed system is the loudest component. A second card makes a HUGE difference in noise.
7) don't consider dual-GPU cards. They run very hot even in idle and are louder than two separate cards (and more expensive).
8) when looking at BENCHMARKS keep in mind that most monitors can only display 60 Frames Per Second.
9) The most important, alterable graphics settings (arguably) are:
- VSYNC (locks screen rate to graphics card, prevents tearing and running the computer hotter and louder than needed. Why run a game at 130FPS when the screen only displays 60FPS?)
- Anti-Aliasing. I hate the "jaggies" 4xAA is often a good setting. There are tools to FORCE AA if it's not available
- 1920x1080 (the optimal resolution if supported)
10) FYI, "The Witcher Enhanced Edition" looks like crap if VSync is not enabled. I have an AMD card (HD5870) and I was able to force VSYNC with "ATITraytools" but not "RadeonPro"; NVidia has a different solution.
11) in general, you're trying to have a game run at a solid 60FPS with the best quality settings. You can monitor frame rate with tools like FRAPS.
Summary:
- read reviews for the links of PSU's I gave. Look for a sale, but don't buy a PSU you haven't researched.
- make sure all components fit
- a second card is NOISY and many games area already maxed out
- graphics card disappears from the market in as little as six months (at a reasonable price)
- high-end setup for reasonable price is 2xGTX560Ti
- if needed, investigate how to force VSYNC if not natively supported in-game, and how to optimize the game overall.
I hope you find this information useful.