But what, exactly, constitues this "unreliability" of high end audio power supplies that you mention? And how would simlpy changing a household power outlet cause a significant change to the sound (via a change in output to the speakers) from said high end audio equipment?
There is no exact answer but many designs are less than adequate and response drifts both over time and due to sensitivity to operating temperature. These design issues create the mystique of burn in and and keeping equipment always on or warmed up. It is possible to design equipment to minimize these issues but that would mean some folks dismiss the gear as "unresolving".
On the outlet side - the countless number of ground loop issues due to poor design, equipment incompatibility and the wide use of RCA (unbalanced) alone explains why unplugging and plugging something back in will often change the response.
In my philosophy, when equipment performs unreliably you should change it. Whilst others see differences in performance as a sure sign that the gear has resolving power. Sales people will tend to propagate the opposing philosophy to what I hold - naturally, rather than admit that something performs a little inadequately (and perhaps take it back) they suggest instead that the buyer consider to purchase an expensive power cord or upgrade the home wiring because the gear is so resolving it requires it. (In other words, there is nothing wrong with the gear you just bought - look for your problem elsewhere. Rather a convenient an attractive philosophy for a sales person.)

