Then you need to research digital pots - but be careful, sometimes the voltage range is very limited, so if your pot has a lot of voltage across it, you may be out of luck.
Quick reply:
It would be interesting to make an actual analog pot control mechanism too. This would mean controlling just about any power supply, albeit a little more slowly than we would like to, but if it is just for setting the voltage one time (other feedback for the actual regulation) then it could be useful. The pot would get worn out if operated too many times of course, but probably no more than if we set it manually.
I guess some sort of geared motor drive or stepper might do it, with basic feedback to determine when the right voltage had been set, then leave it as is until the user decides to change the voltage again.