PSU 12V too high

Jetway MA3-79GDG combo motherboard
Phenom II x3 720
2x2gb DDR3
Galaxy GTX260 896mb
Tagan 500w PSU
500gb SATA
4x8cm fans
Vista 32bit
Not overclocked.



firstly, forgive my ignorance - While I am able to build a PC/fix minor hardware problems, I am by no means an expert.

12V seems to high, way beyond the recommended 5% tolerance level.

Which 12V is this? My 24pin has 12V as does the 8 pin - both are connected to my motherboard.

The 8pin connector was too wide, so I had to get an adapter for it, is this likely to be the cause of the high voltage reading?

I have used Everest Ultimate and HWMonitor to test the voltage and they both gave similar readings - while stress testing with Everest the 12V averaged 14.80.

I took the entire PC back to the store where I bought most of the components - they tested it with the trial version of Everest - which does not give a 12V reading, but they said they tested everything and the system is fine (they had the PC for a week and are likely to tell me where to stick it, if I bother them again, without some really concrete evidence of a faulty PSU)

I am not getting error messages, just now and then the PC turns itself off, and once it would not power up (no fans, nothing) for about 5 mins.

Also the BIOS reset itself once.

The temperatures dont seems too bad - what is marked as TMPIN1 on HWMonitor is marked as aux on Everest.

Is the shop I bought the PSU from really clueless? I did mention to them that the 12V was running at 14.something, but they didn't even use software to check the 12V let alone use a proper hardware PSU volt checker.

I will have to buy one, I don't know anyone who can lend me one.
Is a multimeter better than a PSU tester?
The PSU tester looks easier to use, but can it show full load voltages?