Dual +12V Rails:
Most PS’s today supply all of their +12V amperage through one rail, just like almost every PS manufacturer supplies their +3.3V and +5V through one rail each. However some forward thinking manufacture’s are supplying their +12V amperage through more than one rail, the most common today for PC’s is to use two +12V rails or dual rails.
Why more than one +12V rail?
Electrical isolation for noise and improved voltage regulation. Some devices, usually electromechanical ones having motors, produce noise spikes & voltage fluxuations, these can include pumps, compressors, fans, drives, lights (when turned on & off) and probably TEC’s & Peltiers. By putting these “noisy†devices, that often turn on & off, or at least often change their power (amperage) demands, on a separate rail we isolate them from the MoBo, CPU, Video Card(s) and the other electronic components that are sensitive to noise & sudden changes in voltage. This is a good thing!
Are 2 rails better than 1?
Short answer = Yes. It depends on your system as to weather or not dual rails would actually be of any benefit. If yours is a simple system, with no exotic cooling, large disk arrays or flashing lights, then you would probably not benefit from dual rails.
Do I need 2 or more +12V rails?
Short answer = No. It depends on your system as to weather or not dual rails would actually be of any benefit. If yours is a complex system, with exotic cooling, large disk arrays or flashing lights, then you would probably benefit from dual rails.
What is the difference between dual rails and just using a splitter?
In a dual rail design the PS has two transformer taps and control circuitry for two separate +12V rails. Using a splitter can be very helpful, especially if you split off your “noisy†loads very close to the PS, as this will lessen their effects on your more sensitive components, however the dual rail design would still be much better if you have a lot of “noisy†loads.
Why do all of the newer PS’s from the big names have so much +12V amperage?
The future is going to be much hotter! And I’m not talking about Global Warming, or at least not directly. Back in the P3 & before days, the +12V rail did not have all that many demands placed on it. Today, it is very stressed with lots of demands & in the future, at least until we go to +20V rails (or whatever voltage they finally decide upon), it will be even more stressed with more demands. With the Thermalright XP-90 we have just about reached the upper limits of normal air-cooling. Apple has already gone beyond air-cooling and historically Apple has often lead the way for the PC world. Overclocked Intel P4 Prescott’s can only be kept at reasonable temps with extreme effort. Both AMD & Intel are soon to bring to market “Dual Core†CPU’s, which will require more power to operate and cool than a similar design single core CPU. In the future for “High-End†and “Overclocked†systems we are going to need all of the +12V amperage we can get and it should be on more than one rail for “Electrical isolation for noise and improved voltage regulation.â€
The future of ATX PS's is dual rails, as the "ATX 12 v2.0" spec requires them.
Source
. Ill try atleast 
hyeah:
)