How to upgrade "power cord" on turntable with wall wart?

Give "Uncle" Kevin a call and discuss your needs.
https://upscaleaudio.com/products/sbooster-botw-p-p-mkii-power-supply

I’m all in on upgraded cables, but in the case of a TT power supply, I’ve not seen it make a difference. I’ve tried on 3 tables in my own home ranging from $3k to $20k. The power shouldn’t be reaching the signal path, so I wouldn’t think it could have much impact on sound. 

A TT power cord will have NO effect on sound quality! Stop being so neurotic! As for your other power cords, well many members here know where I stand on that issue.

Yes, can be good for amp and preamp, but for turntable power supply it doesn’t matter in my opinion.

You can upgrade tonearm wire instead, external phono cable (or cartridge if you want huge different in sound)

power cable for turntable is the last thing, really