Heathkit made a nice tri-suppy at one time. The 5V was fixed. What you could do is have a switch for 1.8, 3.3 and 5 or have all three.
Then they had two other 0-20 V supplies. They had a switch labeled independent/tracking, but it wasn't a tracking supply in the true sense, but it made the voltages change at the same time. Thus you can have the setpoints change at the same time. So, you had one tracking/independent pot and another pot for the other supply.
They rounded it out with a meter and switch that were able to select cuurent or voltage for each supply. Rather simplistic.