SPCR

I just found this PSU with thermally controlled exhaust. They claim it's under 12dB. Do you believe them? They don't mention the conditions. It could easily be true at low power draw with cool air going into the PSU, I suppose, but it's harder to believe that it can stay that quiet at the full 360W. They do say that some systems will need an additional exhaust for the PC case.
http://www.low-noise.de/shop/shop.php?id=544
or read a rather poor translation from
http://babelfish.altavista.com/

It may be.
Vantec claims their fan at 21db. I have my seasonic PSU running with one at 850-1000 RPM (thats where it stablizes under most circumstances)
half the speed sounds to me half the noise which is in ball park. All I hear now a day are my hdd idle (180GXP) and air woosh... when I am not using it.

The PSU doen´t have 12db(A)! If you know a bit about measuring the noise-level you´ll know it. Normally a really quiet room for measuring noise has a base-level of 14-16db(A) - so the 12db(A) can´t be measured there.

They just took the manufacturers value which is determined by calculation when the fan is free blowing which means it is not mounted into a PSU or case. If you put it into a OCU the minimum value will be 22 to 25db(A) as a realistic value.

Just take a look at the Verax PSU sold by PCSilent - this power-supply has a real value of 20 to 22db(A) because of the verax fan inside. But be careful in germany there´re some version sold which only have 230V!! The original version from verax has a wide rage input 110-264V. You´ll find the pcsilent pages here: http://www.pcsilent.de/en/index.asp

They just took the manufacturers value which is determined by calculation when the fan is free blowing which means it is not mounted into a PSU or case. If you put it into a OCU the minimum value will be 22 to 25db(A) as a realistic value.

Most likely true.

WHat is OCU? do you mean PSU? If so, it is probably about right. PSU noise is generally ~10 dBA higher than the freeair noise output of the fan it uses due to turbulence, cavity resonance and mechanical coupling effects.

This is not the first post I have seen that rate thier own power supply to be only 12dBA, I have seen it common elsewhere. I really wonder if they just use the Papst 12dBA fan and come up with something this ridiculous. No active PSU is 12dBA, how they measure 12dBA is beyond me..

Dba is a measurement of sound at a given location, not sound energy given out by an object. DBA has worked over the years into a "Ballpark" figure to discern which fans are quieter than with other fans, but it is meaningless from a scientific standpoint to say that an object is x DBA. Maybe that object causes x DBA at a given distance in an otherwise y DBA room, but as those figures aren't given out the actual rating is bunk. It may very well be 12 Dba... at 20 feet.

Of course, my thermally controlled modded Verax PSU is in that ballpark, when mounted in the case, underdrawn, with the sound muffled out the back, and in a 60 degree room... at least compared to other things which have bragged about being 12 Dba and standing unenclosed in freeair.

Is there a real standard for sound energy that could be used / disputed?

yes, well sort of -- sound power in dBA, which is a measure of the total acoustic energy emitted (usually into a hemisphere) as perceivable by most people. It is more of an absolute number -- to use an audio analogy, like watts output in an amp rather than dB output from a speaker.

But sound power is not as easily measured or understood. It too doesn't take into account things like whether a noise pulses or has any kind of intermittent pattern(much more annoying) or is mostly high pitched (much more annoying) and so on and so forth...

...which is why in the end, descriptions by a careful human listener cannot be dispensed with current measurement tools.