Are manufacturer AC cables good enough?

Then what's left? What else can differentiate one power cord from another? 

Well - it's a lot more complicated - to start with, I have found the following affects all cables - not just power cables...

- Connectors - you need quality connectors with plated solid copper pins - my preference is silver plated Sonar Quest connectors - the IEC plugs clamp like a vice

- Quality wires - either OCC Silver or OCC copper - the fewer strands the better, but solid copper or Solid silver wire will fracture if the cable is constantly moved - I now use 4 strands of solid 18 gauge OCC copper for amp power cables and one strand of 18 gauge solid silver wire for source components. I use a different type wire for neutral and ground wires.

- Insulation that has a low Dielectric Constant (D.C.) - Teflon is too high at 2.1 - below 1.5 is best - I now use wire from VH Audio that has mains rated (600v) AirLok insulation with a D.C. less than 1.45

- A well designed cable geometry that mitigates cable related noise - I use a Helix geometry, but there are others to consider.

If you want to see inside a well designed power cable take a look at the Inakustik web site..

https://www.in-akustik.de/en/cables-and-accessories/reference-selection/power-cables/

Nordost also build great cables, but they don’t share their design so openly

I build my own cables, so I can control every aspect - and I build to the requirements of each component.

One power cable does not necessarily work well for every component

Hope that helps - Steve

No it isn't  flawed thinking, it's logical thinking. 

Think of the power cord that comes with your gear as a "courtesy" power cord, just to get you going. @millercarbon explained this very well above.

Whether you are happy with the stock power cords or want to try "after market" power cord, that's all up to you.

Have you every tried to call / email Ayre and ask?

Power cords are included as a courtesy, just like patch cords. You aren't meant to actually use them. They are meant to stay wrapped in the plastic bag in the box to be passed along with the owner's manual to the next guy.

This reminds of a "trick" that the owner of a hi-fi shop does all the time when selling "open box" (returned) items: Oh look... this was not even powered on ... the power cord is still in the plastic wrapper !! 

I've been in contact with folks at Ayre on serval occasions, including a scolding from Charles Hanson for placing a Bryston 10B high-pass filter between my (or maybe his) KX-5/20 and VX-5/20, but never asked about power cords.  I think I understand the logic of millercarbon's argument, and it has altered my thinking about power cables a bit.  Manufacturers do not supply interconnect nor speaker cables, so I rely on Cardas for those.

Thanks for all the thoughtful replies.

db