Great question, one I would like to know the answer to as well!!
I've had both. The Z center has the ability to isolate your preamp, DAC, and CD player. Can only handle medium size amps. A great product. The ultimate outlet cannot isolate your components. It is recommended to have one for preamp, one for digital, and one for amps. It will handle any size amps though. Can be expensive. If done right though, it is simply amazing and in my opinion, outperforms all power conditioners since there is no restricting of the power or sound. Much more open sound.
I have 2 dedicated sets of outlets of which the z center and transport are plugged into one of them and my monoblocks are plugged directly into the other set. I have felt that the sound may be better going directly into the outlet because of now power limitation but am concerned about not having protection from power surges. The z center seems to do quite well but I do not have enough dedicated outlets to do the AB comparisons. Sounds like there may be no sonic benefit of conditioning when you have a dedicated cicuit but you do take the risk of no surge protection.