What is wrong with using the power supply in your current controller? Or did it all go up in smoke?Paul
Does it have to be smooth dc? - I wouldn't have thought so for an electrolytic cell.
Does it have to be variable ? or would turning it on/off with a variable mark-space ratio be acceptable?
If your control board has a biggish conventional transformer for this job you may be able to salvage it.If (as probably) it's a switchmode device, no - and I suggest you don't try and build one unless you have considerable experience in that area.
Question. It is possible you could use the raw rectified voltage to power the cell? you could still PWM the output if you needed variable. And I guess you could use phase control on the input of the transformer.