What is a single and multi rail PC power supply? What is the difference? Do you need to care about it? At the most basic level a power supply converters AC from the wall to DC current for your CPU and other components to use and then an octopus of wires that carry 12 volts, 5 volts, and 3.3 volts of current to your graphics card motherboard. However, how do rails enter into it?
Why the plug-it-all into one spot be considered good? Great question again. Multi-rail power supplies had the misfortune of showing up at a time when NVidia and ATI were both having junk-waving competition to see who can build the faster graphics card without much regard for power consumption. These early multi rail units are sometimes designed with an underpowered rail for the graphics cards or not enough PCI Express connectors, which force the user to use Molex adapters that we are sharing with a bunch of other stuff. This means that the power supply with over low rail simply shut off in the middle of an intense gaming session.
That sounds terrible. I want a single rail power supply. Woo! Do not get too amped up there. Good power supplies are all about going fast, lasting a long time, improving efficiency, and looking good while doing it right.
It is very important that these power supplies work primarily about safety. Any power supply that you should be using in a computer includes a variety of safety cut-offs that will detect dangerous operating conditions and force a shutdown to protect the PSU and the rest of your PC, and even your house. The main ones that were concerned with here are short circuit protection and over-current protection.
The issue is that if your power supply failed in some way that you are short circuit protection does not catch over-current protection is what will trigger your power supply to turn-off. A high-capacity power supply designed to deliver all its power over a single rail could melt away the inflation on its wires and cause a fire before its over-current protection was triggered. However, do not go throwing away your single rail power supply just yet. The chances of all that happening are really very small and funny story but especially nowadays, many power supplies marketed as single rail are multi rail internally anyway. Therefore, it all comes back to what I said before, do not shop based on how many rails a power supply has because it does not really matter these days.
