I believe it all depends on why you use a power conditioner and exactly which power conditioner you are using. With that said if all you are only concerned with is how the preamp sounds you have to try the preamp out of your power conditioner vs your AC receptacle and decide for yourself which you prefer. Your system as well as your physical location and power coming into your home will vary from other peoples systems. In my system a good 3/M power cord connected to an AC outlet would not create a problem.
