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

Changing out an el cheapo wall wart for a decent LPS could certainly help, my ears tell me it made a difference on two phono stages I owned. 
That then begs the question as to whether then changing out the LPS power cord to a much better aftermarket one would yield a further improvement.

Not something I have tried but surely in theory it should have some effect?

I no longer have any gear using wall warts or even a LPS to test the idea out on but I am sure some members here must? 

Well, technically, music doesn’t go through any of those cables. There is no music signal until the speakers generate one. What goes through interconnects and speaker cables is actually the same thing that goes through power cords - alternating voltage and current.

I expected someone will make a comment like this, lol 
It is NOT the same and you know it, because with interconnect it goes from the source directly to the speakers. 

When you supply power to turntable it's just for torque, rotation is stable with whatever cable if the turntable is high quality, now sure what exactly you are trying to upgrade here with different power cable? 

But cartridge coil wire, pins, headshell wire, tonearm wire, phono cable, interconnect cable, speaker cable responsible for the music as the signal traveling from A (source) to B (speaker) through these cables.

The source of electricity is not even in your house and the route is way too long to your wall outlet. I think in my country power cable is nothing special up to my wall outlet, so why the last meter of high-end power cable can change anything ? Please explain if you know it. 

Another analogy:
Imagine conventional turntable with regular cable inside the tonearm (about 25cm) and conventional external phono cable (about 70cm), then change 2cm headshell lead wires for "something special" and try to detect any difference. I doubt that better lead wires can change anything if the rest of the cables is just crap. 

Then replace the rest of the cables (inside the arm and external phono cable) for "something special" inslucing better connectors and listen again. I bet in this scenario you will hear the difference. 

   

It will not make any difference.  If you do however, make sure it is "insurance proof" otherwise if something goes wrong and causes a fire, even though it may have nothing to do with the cable, they will use it as an excuse not to pay.  Not worth it....

You might look up Swagman. I was able to get rid of the wall wart on my Rega turntable with one of their power supply units.

The thing is, some turntables (e.g. many Project ones) require non-DC power supplies, in which case you're stuck with the supplied wallwart or a very close equivalent.