Some history is important here. One of the very real benefits of following Head-Fi is the invaluable feedback of actual users - and this can, and very much has been be used to improve my designs. With the original Qute I could see lots of posters saying that external PSU's were giving much better sound quality - and because of the number of posters, I decided that this was worthy of investigation, as it indicated a sensitivity to PSU quality. Now at the time, Hugo 1 PSU had no change in performance with the charger connected ot not connected; so this implied that the inexpensive PSU was good enough. But Hugo 1 had extra stages of regulation built in from the charger circuit; so with 2 Qute I added an extra stage of regulation, plus more RF filters. Then I used the best PSU possible - a car battery as it has effectively zero impedance, no RF of LF noise, and 300A of current, and compared this to the supplied charger. With Qute I could indeed hear a huge change with the car battery sounding a lot better - richer, smoother, with better depth and instrument separation. But with 2 Qute I could hear no change at all - this validated the improved isolation within 2 Qute.
But still posters were saying that they could hear a change. The problem I have is that I can only report on what I hear - and that is within the context of my listening systems. So does that mean that posters are wrong or that I am wrong? By far the most likely explanation is that people are responding to the PSU affecting other parts of their system; some manufacturers have very little PSU isolation, and are very sensitive to RF noise from switching PSU's - and this is the most likely explanation.
But there are other factors at play, one being placebo (and yes placebo is a very important effect). Secondly, sometimes people prefer things that are actually worse (although it is difficult to imagine a linear PSU being noisier than a switcher - but a quality switcher actually can have lower levels of RF noise than a linear supply).
So it's difficult to predict whether a PSU will give better or worse sound - that's why I suggest trying a USB battery pack and trying for yourself. If that makes no difference, then a LPSU will either be the same, or will actually make the SQ worse by increasing RF noise levels. Do not assume that a LPSU is lower in RF noise....
So I will continue to post only what my experience actually tells me, even if that gets me into trouble; but that of course does not mean my observations will apply in all systems all of the time.