Variable supplies
I've been messing around with this hobby since around 1962 and used to think that I had to have a variable supply ... then a variable supply that would go all the way to zero volts and up to infinity ... then a bi-polar variable supply ... then a triple supply .... etc. However, the only times that I've really needed a variable supply were for theory experiments rather than a practical application. When working with nearly any digital or analog project, I've been very happy with fixed +5, +12 and -12 volt supplies. If I were building by own box, I'd have a raw supply with plenty of overhead and then run several fixed supplies, preferably cascading them so that the lower-voltage regulators don't have to bear the high overhead. Then I'd run bipolar sets for ±5, ±9, ±12, ±15, ±18 and ±24 volts. Plenty of capability, low cost and no frills.
Dean