if this PSU works just fine you can simply replace the fan in the current PSU. To be honest that might be less work depending on what tools or skills you have.

If you really want to swap the PSU then look here:
http://www.outofspec.com/frankenmac/wire.shtml

I would suggest just replacing the fan in your current PSU though. It will be 80mm, 12v. Just get one with the same or higher CFM rating and you should be good to go.