One thing I would say is that a lot of audio equipment these days, even moderately high end stuff, is built to a cost and the power supply filtering and noise handling in general is often not that great (if it even exists at all), which may mean you do notice some kind of difference using some of these gubbins, which wouldn't be there if they'd done a proper job in the first place :s
It depends on what you call "moderately high end stuff". In my mind an amplifier costing more than £10,000 is edging towards high end. An amplifier costing between £3,000 and £10,000 Is firmly in the mid range.....................................so what exactly do you mean ?
Switched Mode Power Supply manufacturers are required to filter mains input but not for the reason you think. The filtering is to reduce the switching harmonics that it creates, otherwise those harmonics would prove damaging to the power distribution network. Once below a certain level they don't care - they've met regulations but mains input is still very noisy from all the sources in the house and even the mains from the street is really really bad quality - often with DC present and flat topped 50Hz wave with harmonics and noise added to that. Above a certain level of noise power companies actually charge money for noise introduced by industry that are deemed noisy.
, if true totally ridiculous. At least post a photo of your amp and speakers