guys, what is the difference between single rail +12v@45A and triple rail +12v@15A.
Most 12v multi-rail units can't output what they add up to.
For most computer user's the difference between multi-rail and single-rail is meaningless, but 3 x 15a @ 12v is rather crappy, I'd go with the single 45a rail in that scenario.
Before anyone comes in and say's " most psu's are single rail anyway ";
Multi-rail designs ( other than those 1000watt or higher ) are fed from a single 12v source that is divided useing OCP ( Over Current Protection circuits ).
In most cases those protections are set higher than the stated rating, example;
750 watt Antec TPN ( currently powering my system ) has 4 x 25a @ 12v on the label ( 62a combined ), by going to the Antec site you will find that the OCP is actually set for 40a per rail ( most unit's are not set this much higher ).
I've also run the same system with a
3 x 18a unit ( Corsair 620HX/ max load 50a, considered to be single rail because of a high or non existing OCP setting )
4 x 20a unit ( TPN550/ max load 45a )
4 x 18a unit ( Odin GT550/ max load 41a )
2 x 17a unit ( Antec EA500S max load 34a, again considered as a single rail unit due to high OCP setting )
You'll notice that the EA 500 goes against what I said above, by being able to ouput the sum of it's rails, it's the one exception that I know of. It's the earlier Seasonic built design, the new revision is Delta built with 2 x 22a / max load 34a ( OCP set at 25a )
Overall, if you're not building a multi gpu super gamer it is more important to worry about quality than number of rails.
I see that obsidian has already thrown in the link, read it.