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.
Chuck
Chuck