Tough subject but power cords do make a difference. The truth is everyone's power delivery grid is "different".....with noise, traffic of RFI etc. So to design an integral power supply to fight the catastrophic power grids likely gets to be more than talk. I have only had one piece of gear in 40 years non-affected by various power cords and that was a Conrad-Johnson GAT preamp. There stock cord ($25) worked right along with other $$$$$cords. I know longer own that pre. but did try many PC's of to no avail. I was amazed by it since it was a new discovery. Never again has that been the case with a power cord.
Hearing is believing?........power cables.......
For anyone who is skeptical about the difference a high quality power cord can make in your high quality audio system........try it.......hearing is believing. About 10 years ago when I bought my first "entry level" hifi system (B&K amp/preamp, Canton speakers) my audio advisor dropped off a Tara Labs Prism power cord. He said just try it for a week and if you don't think it makes a difference just return it. I, like most unfamiliar with high quality cables, was skeptical.......how could a cable 1 meter long from the wall to my equipment make a difference? I put it on the power amp and yes I could definitely tell there was a more defined bass and overall clearer soundscape. I'm a musicians, so I figured maybe the "non audiophile" can't hear the difference. So my brother-in-law who is a bricklayer came over and we did a blind listening test. I randomly switched the Tara, sometimes trying to fool him......told him I switched but didn't........he could tell every time I used the Tara! So I was convinced that it was "wishful thinking on my part or particularly sensitive ears. If you don't think a great power cable can make a difference........take the challenge. Try one for a week and see (hear) for yourself!