Does power cord for desktop PC matter?

The issue with the PC cord is the noise emitted by the power supply itself. If it’s near your audio system, keep it outside of your power conditioner’s clean zone, and consider a shielded power cable, but not an expensive cable.

Usually we say to keep all your audio gear on one circuit to eliminate the chances of ground loops.  The PC, being noisy and potentially high powered, is an exception to that rule.

An inexpensive USB isolator ($40 or less) can be useful in preventing digital or analog ground loops from forming. Doesn’t have to be "audio grade."

Everything matters.  

Whether it's audible or not only you can make that decision.  USB can be quite noisy as it has a 5V line that transmits your computer power to your other devices.  

I use a powered USB hub and a USB power blocker dongle to isolate the computer power from the DAC.  I would think that this would make a bigger difference than the PC power cord but YMMV

Try it, might be tremendous for you. Did not make spectacularly poor SQ any better for me.

I agree that results will vary, but I also believe that everything matters.

Thanks for your inputs fellas.