best power cord for mccormack dna500

steve advises to upgrade but to what. lessloss?
save yourself a pile of money and by a MAC....they are always available at the auction price.
There's no such thing as 'best' power cord for anything. If it exists, then everyone will be using the same power cord.

It all depends what you're trying to achieve, power cord is just a means of 'tone' control, even though some manufacturers try to convince you that their PC are 'neutral', don't buy into any of the hype. The only way of ascertain 'neutralness' is via measurement. Unfortunately human hearings are not created equal, hence 'good' measurement does not necessarily translate into 'good' sound.

Hence when you seek advice on cables, it is best to describe what you're currently using in your system, and tell people what you like/dislike about your current system.
Shunyata Python Helix
Try several and sell the ones you don't like. I recommend Eichmann Technologies Series 2, or Tek Line Cables microReference
I used an Elrod Statement on my DNA-500 with excellent results. Its best to try several - maybe call the Cable Company(John is helpful) and get a few to try from them.
Good luck.

When I had my DNA500 I tried a bunch of different cords.
The one that I preferred the most was the Purist Audio
Dominus (Ferox). It seemed to be nice compromise between
a Shunyata Python Alpha and my Elrod EPS Signature 3.

Another cord I would suggest you try is the new Tek-Line
Reference cord. I prefer this cord to the Dominus and
if you don't like it you can send it back.

whenever someone asks: "what is the best......", i think:

the best is what you like. since preferences differ, there will be many answers. only you can answer your own question.

audition as many as you can at a price point and then tell us.