The newer grey label CX series power supplies are supposed to be better than their orange/green labelled predecessors(which were roughly equivalent to the VS series in terms of quality).I've seen some shifty shopowners trying to convince many unsuspecting buyers to buy older cx series psus by touting them as some of the "best" and the most "reliable" power supplies ever made-and those blokes fell for it as they were not very well informed.
I too had bought a CX 450 earlier this year for one of my computers but faced issues with its output on the 12v rail -it was dipping below 12v frequently in many situations,which was alarming.I made a thread about this issue on TDF.The unit was most likely defective but rather than sending it for rma i sold it off and got a txm 550.
Its quite possible that the CX series psus are not as good as we've been led to believe-therefore it may be prudent to stick to other brands/products as whitestar_999 has suggested.