Hmm, for that system a minimum rating of 500watts is probably about right as you are running two hard drives, 2 powerful graphics card linked, and running on a dual CPU system.
No doubt this is powerful though to run anything you want
Youi are right in looking for a suitable one though, as getting any old one can damage your system in the long run.
Look for ones for example for an SLI based system which will power two graphics cards, and two CPU's. These should be explained in the descriptions of the PSU as they have to mantain solid output when the computer is on to not mess any hardware up, and so, needs to be able to take a rather good beating
Plus, look for some good makes of PSU with those features. I'm sure some people here will be able to help you with that
Though ones with that description are bound to be good (not sure if they need a certificate of some sort or sticker to certify) and probably aren't the really cheap ones.
They are very simple to set up though, and if you get one with that description, or something along those lines, your destined to get enough power cables to suffice your needs
Good luck searching