Nvidia team tested 2 GTX590 with 260.19.21 drivers and they worked ok. The suggestion was again the PSU..and even they wrote me that will suggest and probably drop AX1200 from the recommenced PSU list! However, I reproduced their results with 260.19.44 drivers! The two cards work withholds any problems (at full speed) with the older generation drivers!
Thus, the problem is not the PSU, but 270.xx drivers including the official release!!!!!
My problem now is that I am not able to use my CUDA programs with these drivers...and looking for some temporary solution.
So, what kind of solution can be found? How I can try to "unlock" 270.xx drivers. Could some bugfix to be released? My kernel is 2.6.34-12.3, should I try to update the kernel and actually in what direction to think and what tricks can be applied?
Can we expect Nvidia to fix this, problem??
The conclusion is that currently you can use only single GTX590 under Linux for serious calculations, i.e. GTX590 will be not considered for science until/if this problem be fixed.