Which power cord should you buy first

@salc - as calvin and others have said, power conditioner first. But then followed by server/streamer, then pre, then dac and last, amplifier - seemingly counterintuitive, I know, but it’s all about the source, as evidenced by the biggest changes to sound realism. The dac isn’t part of that source, it comes after the server/streamer, and the pre is the first point of amplification, which is a source of sorts. The dac comes after the pre, only because it sits before the amplifier. I have never heard sound quality benefits from good cables to amplifier the way I have from the server, pre, and dac, in that order. And if your server/streamer has digital preamplification, then all the more reason  : ) - just a different take on a long debated issue.

In friendship - kevin

Which of your components is going to inject the most electrical noise into your power supply? Most likely culprit is a class D amplifier, followed by a computer! Least likely might be a turntable, provided it does not have a switching power supply.

Only one thing matters to me E=IR  

NONE

Salc

First I'd make sure to have high quality power receptacles, something like the Furutech GTX-D (G gold or R rhodium), Oyaide R1, or even the cost effective Acme Audio Labs silver plated 20 AMP cryo and CFC coated at $60

Then as others have suggested; power conditioner, streamer, DAC, preamp, and amp. The signal components don't need as heavy a cable, so usually a little less expensive; the preamp and amp I prefer a heavy gauge, something like 11AWG or less.