That PSU "will not" be suitable for an SLI system. To run an SLI system you'll need a PSU that has a (24 PIN) connecter. The extra (4 PINS) are added specifically for PCIe & SLI.
If you are currently only running (1) GFX card not SLI'd then that PSU will be fine. But, add another GFX card and you should upgrade your PSU to something with DUAL 12v Rails, SLI ready and no less then 500watts.
Here is the only thing that I recommend:
PC Power & Cooling Turbo-Cool 510 Express/SLI - http://www.pcpowercooling.com/produc...hp?show=T51SLI
Yes it's expensive but the quality and reliability is top notch. There are other PSU's that would probably do just fine. May-be someone else could recommend one. I only recommend PCP&C because that's all I use. For obvious reasons...