What can cause bad 12 and 5 volt rails?

My 12 volt and 5 volt rails were incredibly bad. So i i assumed my old psu a chieftec 340 watt with 16amps on the 12volt rail wasn't cutting it. So i bought a new psu. Sadly the 500w NeoHe was sold out and i just wanted a psu so i went for a bit cheaper one. and about 16 amps less on the 12 volt rail the. an Antec smart power 500w.

I've connected it and still the voltages it measured were icredible off target.
So i measured it again with a multimeter to be sure its not my mobo. And still
the 12volt rail is 12,6 volt (not 12,06) and the 5volt rail is 4,8.

My comp is pretty low end these are my specs.

2x512mb cheap *** corsair value memory
1 7200rpm seagate harddisc (can't bother to look what it was)
an asus a7n8x deluxe motherboard
an amd athlon xp 2500+ (running stock :\)
2 dvd burners
and a asus v9999ge (6800nu with 256mb gddr3) with unlocked pipes.
i disconnected all casefans in my case to test things out, and it doesn't change the voltage. =\

What could it be is the psu faulty? =\ or maybe i'm only using 1 of the 12 volt lines instead of both. What have i done wrong :X.

my +12v is high (12.4 approx) but the +5v is not much past 5 (5.03-5.10 avg).

Your CPU is drawing mostly from the +5v line. Your video card should help to reduce any possible low crossload problems from a high +5v/low +12v.

You should be fine, though the +5v is a bit low. So long as it doesn't dip below 4.8v.

You are only using +12v1. 12v2 is on the 4pin +12v connector, which your board doesn't have (unless they've changed it, my a7n8x deluxe didn't). It should be fine though, as they are somewhat independent and you aren't taxing the capacity of 12v1.

i'm planning on buying a new mobo and processor in some time. Probably an athlon 939 socket. What motherboards have the connection for the 12 volt line? so it will use the additional 12 volt rail

all new boards have the 2 by 2 12v extra connector

to the forums.

Any recent motherboard will at least have the 4pin +12v power for CPU. All S939 boards have it. Some have the 8pin like some of DFI's ATI boards.