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

lewm, I’ll admit that if you redefine outside the signal path to mean in the signal path then yes, you are right. Word games aside the point is all these things really do matter. And not subtle, but a lot.

OP- full disclosure. When talking about platter, plinth, motor, bearing, motor housing, etc. and saying "all these things matter" there is the possibility of misunderstanding. "All these things matter" not because someone said somewhere once upon a time. "All these things matter" because they have each and every one been tried, one at a time, and been shown to matter. Its how the Miller Carbon Turntable was built.
DYODD. https://systems.audiogon.com/systems/8367

It makes a difference. When I bought my Technics SL1200G I started with the supplied power cable. I had Rob Fritz from Audio Art build me a cable for the turntable. Once I inserted it into the system, there was an immediate and noticeable increase in PRAT. Going back to the stock cord, the PRAT diminished noticeably.

Please notice OP there is a pattern. Those who have actually tried and done all say it matters because they know from experience it matters. Those who have not done make grand pronouncements devoid of any actual knowledge, let alone experience. Its rote repetition. Repetition without comprehension. The proper response to them is, "Polly wanna cracker?" As opposed to stereo5 and me to whom its, "Well now, good to know, I will have to look into that. Thanks!"

Speaking about turntable power cable in general
Not sure about US standards, but could you explain how a short piece of POWER cable connected to TURNTABLE compensate for x100 times longer cheap power cable going from the wall outlet somewhere outside of my flat and connected to console in my house where we have 14 apartments on 7 floors. Why the last piece (1m) of power cable is important for turntable while another 100m of power cable is not important?

Thick cable that you have with your desktop computer is bad? Cable of the same thickness hidden in the walls in our flats. So to improve a 100m cable you just have to add 1m of different cable on one end according to this logic? And this is the cable that just supply voltage to turntable motor that rotate the platter.

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

I use all my turntables with stock power cables, i have expensive power cables for some of my amps, preamps. Manufacturers supply regular power cables. BTW I’ve seen the power cable behind my wall outlet.

I can get the idea of power conditioners and pure energy devices, but why 1m of a better cable connected to 100m of conventional power cable makes any difference? Please explain this phenomena.

Would you like to replace another 100m of the power cable behind your wall outlet then, and how far you can go ?

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.