best power cord for digital switching amp

There is no best.

Select a few to try and listen for yourself. Decide which you prefer.

I suggest buying used, and buying cords that are popular and in demand. Doing so will limit your losses as you resell the cords that came in second and third.

There is special power cord made specifically for powerful switching amplifiers by Spectron Audio. See - http://spectronaudio.com/remotesense.htm Thunder - not expensive, about $600 and FANTASTIC!

Good Luck in Your Search
Rafael,
P.S. Elrod Silver is probably better but cost $2,900

You can get 98% there with a cheapo Belden. The important thing, regardless of price is that the power cable is fully shielded. The Belden is shielded with both woven and sheet aluminum.