How to replace hardwired stock power cord ?

Even the most dirt cheap power cord will be a lot better than what’s on there now. That being said, its a 20 year old CD player. Worth nothing new, worth less than nothing now. Certainly if you have even $100 for a power cord you could get a lot more for your money just buying a better CD player. Or even $25. I mean there are probably better CD players on CraigsList listed under FREE STUFF and just sitting by the curb.

But the urge is just unstoppable and you can’t bring yourself to just solder a better power cord onto it (which is the way to go) then next best is what viridian said.

Oh, and what do you know:
https://seattle.craigslist.org/search/zip?query=cd+player

Just unsolder it and take a dremmel tool cover up things 
and cut out for of good Furutech IEC , 2 small screws after drill holes , done , with captive power cord unsolder and solder your own in . I have done this several times much better performance ,

Cost of a Furutech IEC and a Dremmel tool you may not own, I’d just buy a decent used PC, take off the female end and drill out a larger hole and buy a new, larger strain relief from Michael Percy. Page 21 - Cord Strain Relief: Collet Type. That’s what I would do. Pull the new cable in as far as you can and solder back to power supply.

https://www.percyaudio.com/Catalog.pdf

Haven’t looked up your Nak but my guess it’s only a two prong plug. I agree add a shielded cable so look up digital two conductor power cable on VH Audio site and buy a Hubbell Hospital Grade male plug and tie the shield to the ground at the wall receptacle. Easy project. I use the VH Audio digital cable and it’s very good. Be surprised you’ll find better for the money. Shielded twisted pair.

https://www.vhaudio.com/wire.html

https://www.vhaudio.com/images/shieldedtwistedpairbulk.jpg

The VH Audio cable mentioned will likely work in the existing strain relief if you’re careful taking it out.

I have had really bad luck with Furutech for speaker connectors, so I no longer go near the brand, but there are a lot of fans.

You may also look to see if you can find Cardas in the right form factor.

If you eliminate the socket, you eliminate one more contact location, that's why I feel that hard-wiring a new cable is a better option. I always recommend shielded cable for digital, as I think it minimizes the chance of radiating noise back out.