Originally Posted by UnexplodedCow
I think many people also forget the multiple 12V rails many power supplies use. Some of those use virtual rails, too, but it can still cause issues. I prefer 1 (2 at most in the case of the HX1000) 12V rail. They may not reach the absolute efficiency of multi-rail designs (yet), but are far easier to balance loads on, and I believe it also shows better design, as engineering a heavier duty circuit is always more difficult, and requires more expensive parts instead of building multiple small-power circuits with cheap parts. I'm waiting to see more redundant power supplies come to market for the everyday power user.
Actually, all multi-rail PSU's (except the one you have, which is really 2 separate PSU's in one) use 'virtual' rails, if you want to call it that.
In fact, multi-rail and single-rail PSU's are identical internally with the sole exception of the presence of over-current protection circuits placed on various groups of cables coming out of the unit (these OCP circuits define the 'rails'). 'Rails' are just a safety feature, not an architectural difference in the basic PSU design.
Externally the only difference is that multi-rail units will generally use higher-gauge (thinner) wiring vs. a single-rail equivalent. This is because the OCP's protect against any more than the specified wattage being pulled through the set of wires that's governed by that OCP.
With a single-rail unit you could theoretically pull the PSU's entire capacity through one molex plug, so all the wires need to be of a gauge that could handle this possibility w/o catching fire.
And 'balancing loads' is not a problem on multi-rail PSU's these days (was different in the early days) unless you're doing strange stuff like running TEC units or have a bunch of molex-PCI-Ex adapters running your video cards. As long as you use all cables as they're originally intended, there's never an issue in terms of trying to pull too much juice out of any one set of wires and tripping the OCP.
Lastly, multi/single rail has no effect on efficiency.
Don't mean to sound like I'm blasting you man ... a lot of people have the exact same misunderstanding ... I did myself back in the day until someone set me straight Edited by brettjv - 4/15/11 at 6:20pm