Which power cord should you buy first

I bought 10 awg shielded power cable for my power amp first and, gradually, 12 awg or 14 awg shielded cables for the rest of the gears. My Monster power conditioner has a pretty beefy shielded cable so I don’t worry about it.

stock one is technically used first.

When I first started, I bought the Amp power cable first. As my system evolved, I Introduced a Saturn Audio 103C power conditioner, and an isolated 20 amp CCT. that power cord from the wall to the PC was critical. then everything plugged into the PC. I purchased a cable for every component after that.

Dac , power cord  the dac being the source provides the music coming in you want this at its best for you cannot correct it down stream .

My experiments show a certain amount of system dependency, but all benefited from power amp being fairly high up the list, afterall.  You are taking a fairly small signal and multiplying it with a voltage / current that you want to be as clean as the small signal you are multiplying.