The term 'Rails' is a marketing gimmick.
All it is, is a multi-channel PSU. If you've ever built a power supply from scratch before you'll realise all they did was duplicate the regulator circuit after the bridge rectifier (ac->dc converter stage)
So if capacitors start leaking in the one circuit/channel, it doesn't directly affect the other ... opposed to splitting parallel feeder cables from the same output circuit.
Bottom line is, the transformer only gives out X amount of power, no matter how you draw from it. There's no dark magic inside. Sadly.
This is essentially a DC power supply in its simplest form:
All that these fancy PSU's do is create another smoothing/regulator channel. I must say I like the idea, because if one channel goes, you can still power another one ... and you are less likely to have harmonics filter through. Still, grossly overpriced for components that you can buy for 50c a piece.
