I guess I did. But my point was that the smps600/nc400 combo was unaffected by the cords (both subjectively and objectively). What properties do you think your 3 superior cables had that the others didn't, and how did they affect the PS and amp?
Julf, I'll take a stab at this, since you appear to be honestly asking for some explanation/speculation on power cords and class D/SMPS. I tend to agree, that given adequate gauge, and solid connections, and considering the nature of SMPS, that the power cables probably do not make the SMPS work any "better", or the amp(s) themselves sound different. But I do believe the power cables used in this application can make the system sound different:
The SMPS do spray out a bunch of high frequency harmonics, despite their filtering (even the simple AM radio test will demonstrate this). The power cable can affect what happens with these harmonics. A power cable could, for example, act as a good antenna broadcasting these harmonics to be picked up elsewhere by the system where they could then intermodulate with the analog signal. The harmonics could travel back through the cable, and then on to the AC input side of other components, again with deleterious results. I have experimented with different (mostly DIY, but some high end product as well) cables on class D/SMPS amps, and have noticed differences, and I have come to the conclusion that cables well designed to not broadcast RF (by geometry and/or sheilding) and with RF damping included generally work well for me. Of course, different cable designs will attenuate/sheild different frequencies of RF differently, and different systems will respond (or not) to RF degrtadation effects differently, so individual experience will vary as well as to the subjective results. I suspect that these same causes/effects are responsible for peoples' experience with power conditioners and class D/SMPS amplifiers.
Of course, really good spectrum analysis of the AC line and testing with different power cables (and power conditioners) could tell us if my feelings are correct, but who has a really good spectrum analyizer capable of that? Not me, unfortunately.