Here's some additional information about 12 volt power.Industrial power supplies may have several 12 V connections. The hobbyist should understand why this is a common practice in the industry. Is not just simply a case of getting more current through the wires and connectors. Rather it has to do with stability of the system.
The switching power supply can have any number of outputs. Each output is a separate sub assembly that delivers the desired voltage to a pair of wires. The sub assemblies do not all have to be grounded together. The return wire can go out to the motherboard and at the motherboard it is hooked to the common.
For the amateur enthusiast the reason for this may not be obvious. But there is an issue regarding stability. By having each unit with separate ground return wires it improves the stability of the system as there is less interaction between different devices that suck power from the 12 V lines. Or, to put it another way, it helps reduce the voltage swing on each supply. That's why they do it.
If they needed just a huge 12 oh power supply, that is what they would build. But for the computer stability is very important. Small variations in voltage can cause unreliable operation in some parts of the system. By using separate 12 volt sub assemblies, the stability can be kept
within 2% or even better.What I'm trying to say is this. If the design calls for 12 V in four different places on the motherboard, you have to have a power supply that does deliver the four 12 volt independent power from sub assemblies.
Some hobbyists have posted another places that you can just simply type all the units together and hook up to a huge 12 V power supply. That's not true. It was not designed that way for a reason. It has to do with stability. Muck around and try some hacking and you'll end up with something does not work reliably.
Just for informational purpose. 
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