Power cord replacement where first?

I would ask which of the products, if any, came with an adequate cord. Are any of the ones you have closest to the mark? Maybe some are in greater need of an upgrade than others? Or are you asking: Assuming the same fair but not great cord for each, which upgrade would have the most marginal benefit (i.e., bang for the buck)?

Slightly off topic, but I have purchased about 8-10 cords over the past 3-4 years. I have found almost no correlation between cost and quality (however subjectively determined). For example, there is a great cord from a company called Tube Audio Design which sells a great and usable cord for $30 (discounted heavily). I have paid $350 for a "better" brand and not liked it much. Very hard to quantify.

PS I've no affiliation with the co. referenced. Only contact was buying the item with my PayPal acct.

Do a search on shielded versus non-shielded then experiment.

Looking forward to your impressions regarding which component you think has the best result with the PC.

The digital source is what I'd suggest, the upgraded power cord will both improve the input to the CD player and also filters the digital nasties that are outputted into your power supply from the CD player. Two for one. None of the other components need both input and output improvements from the PC.