I used the word "buffer" to illustrate the separation of the AC source from the DC output. I realise it's not the exact, proper way to describe the situation electronically. Despite this, I stand by my assertion that as far as the amplifier circuit is concerned, it is powered by DC and provided the power supply is doing its job, the AC source energy has no influence on the operation of the amplifier if it is within specification. As to EMI and RF filtering, both can be addressed in the power supply circuit. In addition, a mains supply cable is not part of the signal chain and does not require a physical shield, there is no benefit whatever to incorporating a shield into its construction. The OP on this thread included some graphic evidence that there is no measurable difference between mains cables. It's no surprise that in a sighted test, the listener will be predisposed to hearing a difference if a plain OEM cord is swapped out with a ridiculously elaborate (and expensive) one. This is a subject we have worked through at great length on this forum.
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Another thing is that we almost always agree on is that if someone perceives value in this sort of accessory and that's how they want to spend their money, knock yourself out! However. where there is absolutely no support for an item like this to beneficially change the operation of the equipment it is connected to, we call that out.