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

If it’s a wall wart you can’t change the mains cable on it as it hadn’t got one. You could try an alternative if you know what it is supplying the table, easy enough if it’s AC and you know the voltage and frequency. As a first test that won’t cost a penny try the supply you have in different positions on the power strip, assuming you’re using one. If you can hear position make a difference than playing with the supply might too. A larger transformer maybe if that’s all the wall wart is. Naim used to make a supply for the Linn LP12 that was just a large toroid in a box and a phase board that went in the deck. I used to power a Manticore Mantra from an isoformer instead directly from the mains to good effect but when I bought a Townshend Rock with a Merlin ps (producing a synthetic sine wave) the isoformer degraded the sound when I put it before the ps.

Replaced the WW that came with my Clearaudio with a 12V linear power supply from Jay's Audio.

Did it right after I bought the TT and never tried to A/B them. 

Just felt it would be better to have a bigger and more stable power supply feeding it.

Now that I have so much spare time on my hands, I may build myself an upgraded "umbilical" power cord.

And I can not say enough good things about Jay's Audio. Great customer service, shipping and product. 

No, not affiliated in any way with them, just a very happy customer!

chaster-

I just don’t get it. Maybe i’m stupid? 

Wouldn't rule it out. Which if you think about it is the crux of the problem. You have ruled it out. Why? Because you can't explain it. 

That is one very stupid reason. You may not be a stupid person. We give the benefit of the doubt. But you have picked one very stupid reason, which does not tilt the odds in your favor.

There's a serious issue here you will do well to try and understand. There is a difference between the existence of a thing and the ability to explain the existence of a thing - and the one does not rule out the other. 

Got it? No? That's a shame. Odds tilting yet again. We will try another approach. 

The Earth is round. Possibly (benefit of the doubt again) you agree. But why? Looks pretty flat to me. 

Never mind. Here's the question: The Earth being round, does it have anything to do with anyone's ability to explain why its round? 

A whole bunch of people have made the comparisons and consistently reported that power cables do indeed sound different. You claim the right to say they are nuts. Why? Please explain.

It might be worth looking into whether there's a U.S. voltage version of this - https://www.decoaudio.com/deco_audio_project_unibox_power_supply.html