THE WALL---Why?

There are many types of PS Audio Power Plants so I'm not sure which you are speaking of. Personally if I had one of these http://www.psaudio.com/products/p3-power-plant/ I'd certainly plug my amp and everything else into it. I don't by the amp into wall outlet theory. In my case I've taken a far less expensive route: Dedicated (separate breaker) 20 AMP wall outlet >>> Emotiva CMX-2 >>> Panamax MR-4300 >>> all audio video equipment. Works well for me. Doesn't limit current by any practical standards, although technically this is not 100% passive but is extremely close to 100%. Also, I'm using SS equipment and I'm uncertain if this would work as well in a tube situation.

@cleeds I'm in Freeport Long Island, which offers among the best electrical service in the country. Despite that I'm on a dedicated outlet, voltage varies - on an intraday basis - between 116 and 123 volts inclusive. Naturally I cannot detect any audible difference. Not entirely sure, but I thought 120 was the goal/optimum (although that likely varies a few volts from component to component).

@ahendler not trying to be argumentative, but I'm of the opinion filters are not meant to improve the sound. Not to say that they can't, but if they do it usually would mean something was very wrong to begin with. I think ideally any improvement should be subtle at best and the maximum benefit is realized in your equipements "health". 

Hi Alan. As I mentioned in my previous post, the primary purpose is to provide voltage/current in such a fashion so that it improves system component "health" (operation, efficiency, etc.). I've noted that not all manufacturers of filters make any claim about sound improvement. Also, consider what many on this forum and in this thread in particular have noted, which is in their opinion it can (paraphrasing) be a detriment to the sound. I suppose this is why those individuals plug an amp directly into the wall outlet. The concern shouldn't be less available current as virtually every filter manufacturer claims their product does not limit current. Depends on who you want to believe I suppose. Also, and as I've stated previously, if there is a sound improvement it really should be very subtle. If you're noticing some major improvement - as some tend to describe - I'd venture to say something is fundamentally wrong above and beyond power concerns. just my .02.