Funny, I tried a Power Plant Premier and it made virtually no difference in my system. I then tried a Shunyata V-Ray II and it made a huge (positive) difference. I guess it depends on the system and the quality of the electrical power.
Audio is not an exact science. The term Voodoo is more approprate. I used the highly acclaimed Furman Reference 20i before getting a Powerplant and it did nothing for my system at all. Having said that, I may need an additional conditioner if I decide to reconfigure my system and will probably try a Shunyata for camparison against the PS audio P5.