[BrianG]

I don't know if I would just tie them together. I tried it on one of mine and I noticed that one of the 12v supply output FETs got quite warm. If one of the supplies is even a little higher voltage than the other, there will be current flow and cause the slightly higher voltage one to work harder. It's not like batteries where the slightly higher one will drain down until they match.

Also, many of the dual 12v supplies have 12v rails that don't match current-wise. One will be rated for say 15A, while the other will be rated for 17A. I don't know why and it doesn't make much sense.

A supply with a single 12v supply has a higher current capacity than either 12v rail on a dual supply. The single supplies are still made, it's just a matter of looking at the specs, or better yet, the label on the side of the power supply itself. If there are two 12v supplies, then there will be the max current ratings for each. Pretty easy to tell.

Newegg.com has good prices, great return policy (although if the wires are cut, that will void the warranty), and have good pictures usually showing the label on the PS. Plus, you can read the user reviews to see if one is prone to problems.