Youll need a Power Supply which is marked as ATX2 - they have a 24 pin power connector. Most, if not all, cheap PSUs are not ATX2, so you may as well not consider them! Antec/Enermax are good brands.
I think what you're referring to regarding the 12v thing, is Dual 12v rails. These are not connectors, but it means that these units donate one 12v rail directly to the CPU, the other powers the rest of your components.
This basically gives your CPU a constant good power source, and is therefore a nice thing to have! If you're looking at units that have these, then you're looking in the right place quality-wise!
Just as an example of what you should be looking for, This is an excellent unit!