Power Supplies: Single Rails vs Multiple Rails

Multiple rail PSUs cause
problems when one rail gets overloaded and shuts the PSU down. For
example, if a video card pulls 18A from a PSU that has two 15A +12V
rails, it may overload one of the rails and destabilize the PSU.

Thus, in most cases, a single-rail PSU is almost always better than a
multiple-rail one. But understand that all single-rail PSUs are not
guaranteed to be great. Only high-end PSUs that deliver large amounts
of power on a single +12V rail can be classified as excellent PSUs,
since they typically have better internal parts such as high-quality
Japanese capacitors from Rubycon or Hitachi and sturdy casings and fans
that do not vibrate dangerously. PC Power & Cooling, Seasonic and
Corsair are among the best companies that produce units rated as low as
450W with single +12V rails.

The ultimate thing to look for in any PSU is the total power supplied
on the +12V rail(s). If it's a multiple rail PSU, divide the power
value by 12 to get the amps provided in total across all the rails. A
PSU with any documentation that does not provide this information is to
be avoided. The same goes for a PSU with no documentation at all.

Lastly, look here for more pointers on how to buy the right PSU for your system.

so get power up ur pc

cheers!!