A generic 12v 20a power supply that s19 pro needs costs a mere $60 where i live.
The miner does not use a generic 12v PSU and what they use delivers a lot more than 20A. 12v*20a=240w so not even close to the over 3kw the s19 pulls. Modern miners use variable output PSU's that adjust the voltage to between 15-20vdc at well over 150amps.
Ah then to jerry rig something together one would need two power supplies with the outputs as mentioned in the link below, one to power the chips and the other one to powet the control board.
https://shop.bitmain.com/product/detail?pid=00020210302152412332Xrq3G3E60644Still, not outta the equation considering that the variable output power supplies are going for quite cheap on chinese websites.
The main chips receive around 12-15v at 233A apparently and the control board is 12.3V at 15A (i think)