Where to use aftermarket power cords?

I think a reasoned approach would be to purchase a cord of your choice and try it in your system in each of the components you mention. The impressions you get will be based on your experience with your system....not anyone elses.

The previous answer is correct as far as it goes, but I don't think that's what you're looking for right now. When I replaced my PCs I started at the source. I enjoyed the improvement so much I continued all the way back to the amp.

I tend to think the maximum improvement will be recognized by starting at the source.

In my opinion, they're equally important. It really depends on how the power supply design in each unit.

I'm guessing that you have the budget for a single good cord and want to put it where it will do the most good. You can certainly have fun swapping around, and draw your own conclusions, but IMHO Nrchy is on the money. With this particular upgrade, the most improvement in my system came when I put a high-end power cord on the digital source. (With transport and converter separates, the DAC is usually the place to put the cord, but in one of my setups the opposite was true.) The preamp comes next in priority after the source. Changing the cord on other components may have a less noticeable effect.

I found that I got the LEAST impovement using it with my digital front end.

I have had two different digital front ends; a Krell/EAD combo and now a Marantz. The result was the same with both.

The rest of my Krell gear; preamp, x-over, and amps, were all greatly improved.

Richard