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I wonder if a part like this would work: https://aliexpress.com/i/4000307508670.html ? This is an external part so I'm not too sure how you'd connect it to the casing.
As long as that PSU is externally controllable/programmable, it is exactly what is needed. Of course readouts of voltage & current are not required 
The key point is one needs to know how to communicate between the controller and PSU: Is it digital (I2C) or analog (0-10v = 0-100%)? Does the PSU report back to the controller to give basic status and actual voltage & current output?
The control board and the hash board require separate voltages. In my opinion the best bet would be to spend the $300 to get an actual PSU thats meant to work with the miner. This then means that the only component thats not factory is the hash boards. The hash boards simply have some SMD diodes for reverse current protection and some capacitors along with the BM1398BB chips.
Now speaking from experience, i've replaced hashing chips on antminer s17 pro in the past and they tend to work normally, the hash board does not look much different than s17 pro's hash board so i am pretty certain that the chips themselves are not tied to the control bobard in any way.
If someone manages to help with copying a hash board pcb for cheap then we're basically looking at an s19 pro for around $2000 if not cheaper.