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

Absolutely, some much better than others. In the past I have used top cords from TekLine, but have mostly switched to Wire World, who calls his 'power conditioners'

They certainly increased the overall performance of my 2 Emerald Physics EP 100.2 SEs

When we sit listening to our stereos, we can’t literally see photons or electricity, but we can hear differences. 

But, to the OP, I have a Triode Wire Labs “Digital American” power cable on order to arrive this week. It is designed specifically for class D sources, amps. Supposedly helps to reduce brightness of Class D and help sound more organic. 

Will see. Check it out on their website. $500. 30 day return policy. 

If its expensive then you will trick your mind into thinking there is a difference!😆

There is no such thing as "directional" alternating current - period.  Mr. Tesla proved that 100 years ago.  

KW6 - I think it's the other way around - "it's expensive in order to trick your mind into thinking there's a difference".  A fool and his money....