Can a power cord increase the resolution of an Class D (SMPS) amp by more than 5% ?

azbrd,

I totally agree with you. I have heard minute differences with some upgraded (and somewhat inexpensive) power cords. Most of that being tiny variations in (audible) frequency response. I was just bringing to attention to the large variation in SQ that Mr. Fremer claims to be hearing. It is most definite that I do not agree with him. But that is just my opinion. I cannot afford to dish out several thousand dollars for power cords and even if I could, I'm not sure I would....

I have heard minute differences with some upgraded

Could that maybe read "I think I have heard minute differences with some upgraded  (and somewhat inexpensive) power cords." 
If so bet in a blind A/B that "think" would be even more emphasised to the point of maybe the wind changed direction, or the amp came up to it's heat stable bias setting.

anyone who buys or considers buying a >3K power cord should have their head examined and fully deserve to have their wallet drained.

I  just looked at these and it's $5k for the 2mt one and $7K for the 3mt one!!!!!!!!!!

Cheers George 

IMHO, If one was to consider spending such funds on (1) AC cable per component, the superior choice would be to either hire a competent electrician or DIY (if so inclined) and have your AC wiring upgraded to multiple dedicated AC circuits, a new 300 - 400 amp service, new isolated ground, hospital grade, 20 amp receptacles and dedicated copper ground rods. One would probably have enough left over to include multiple data center grade double conversion ups’s, surge suppression in the service disconnect and a "sharpie" to write arrows on the romex cables. With the exception of the "sharpie" that is what I have done to connect my components to. It was a DIY project and cost about $6k, easily one of the best investments towards better sound I have ever performed. I also called my local power utility company when I installed the new service as they would have to connect their service wires to the new service panel, I showed the service guys my audio equipment. They installed a new transformer from the 3 phase power they provide and installed new copper wiring from it to my new service. I really lucked out on that one but I HAVE been paying their company over the decades. What I am trying to illustrate here is don’t hesitate to ask your power company for better AC power. Additionally, don’t forget to clean ALL of your connections every 6 months or so to prevent oxidation from building up. It will not make anything "sound" better but you won’t compromise anything to poor or oxidized connections. I get a "warm fuzzy" from doing this. YMMV.

ampzillaOne

You mention "dedicated copper ground rods", are you suggesting these be installed in a separate location?  If so, that would violate code and create a nasty ground loop potential.  Other than that I very much agree with your suggestions.  For my setup I have a dedicated 20amp circuit for my audio system.

No, I have (2) 10' copper ground rods bonded together and then connected to the breaker panel ground as close as physically possible.