Thank you but what is a DC unit and what's the CV and CX
On DC-DC PSUs(like the CX series) you have 2 conversion stages... from the first DC stage you get 12V and in the second stage you're getting 5V&3.3V from 12V.
Modern systems power draw is on the +12V mainly... +5V&3.3V load is little, but that doesn't represent a problem since they're fed up by the same +12V rail(2nd DC stage).
On group regulated units like the CV you mentioned +12V & +5V are regulated together(3.3V is regulated independently).
That represents a problem on modern systems, because the +12V is loaded heavily usually, while the +5V is seeing next to no load in comparision... in this case +5V won't be kept under control, going out of the ATX voltage spec... that's no good for your components lifespan.
That's the reason why you should always go for DC-DC PSUs instead of group regulated ones nowadays. For the same reason I'm advising you to get the CX(DC-DC) instead of the CV(group regulated).