By the time you've bought all the components, put everything together and gotten things to sort-of work, you could have bought a commercial unit. For instance, on ebay, the Tektronix PS503A is a triple supply: ±0-20v, current limiting up to 1 a and +5v, fixed, 1 a. The variable supplies can be slaved together at any ratio and made to track one another. Put one in a TM504 power module along with a DMM (e.g., DM502), frequency counter (e.g., DC503A) and an audio oscillator (e.g., SG502), and you have quite a bit of power in a very small, inexpensive space. You can probably put it ALL together for around $250 US, and far less if you bid on and get "junkers" to repair. Tektronix equipment is VERY repairable and worth repairing.