What is the difference between "Single-rail" and "Multi-rail" power supplies?

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Personally I like single rail designs, especially when you are looking at lower wattage supplies, because if you get in to a situation where you are using the power in the upper limits of the device then generally you have to be sure half of your components are on one rail vs the other but sometimes you don't know which connecters are attached to which rails (Generally the PCI-E will be on one, where other things are on the other or some logical separation).

Also, in some configurations in multirail designs you end up that your machine is fairly efficient but you want to jam a big video card in there... I ran in to this with a 6870 a while back using an Antec Earthwatts 380. The machine as tested peaked at about 120 watts the...
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Traciatim

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Personally I like single rail designs, especially when you are looking at lower wattage supplies, because if you get in to a situation where you are using the power in the upper limits of the device then generally you have to be sure half of your components are on one rail vs the other but sometimes you don't know which connecters are attached to which rails (Generally the PCI-E will be on one, where other things are on the other or some logical separation).

Also, in some configurations in multirail designs you end up that your machine is fairly efficient but you want to jam a big video card in there... I ran in to this with a 6870 a while back using an Antec Earthwatts 380. The machine as tested peaked at about 120 watts the additional of about 140 for the video card would bring it up to about 260 which should be fine... but there is no good way to know how much of that power would come from the PCI-E connector and how much from the slot, and you'd have to use adapters to get the 2 PCI-E connectors. Each of the rails are only rated at 17 and 15 amps, so max 204 or 180 watts... So if 80 of those extra 140 watts on the video card came from the same rail as the rest of the machine the power supply would likely shut down as the first rail would be over it's capacity. I didn't want to chance the configuration so I had to replace the supply.

So the TL;DR version is... it depends on the supply design, and the usage... but for most intents and purposes if you are buying a big supply for your machine anyway you don't have to worry about it.


 
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