Latest P.S. Audio Ultimate Outlet????

Hello Frends,
with all the used ultimate outlets conditioners out there, how do you know you are buying the latest one???. Are the new ones much improved from the older versions? or about the same. Which one would work best for my krell, power amp. Are the 20amp versions consider old versions. Let me know again thanks for your help.
If I were buying a used one I would ask the seller for the serial number then ask PS Audio which version it is. I understand the UPC-200 is improved over the older UO version. I had a UPC-200 and did not like it so I sold it. I have never head the older UO version so I have no frame of reference from which to compare. You really need to compare for yourself as the need for power conditioning is very subjective. If you try it and like it then so be it.

Did the design change? Not that I know of.