2 Single Output Bench Power Supplies vs One Dual Output Supply

I would advise you to use 2 adjustable power supplies with current limiting. Especially if you are new to electronics and are a mere human, you are likely to make mistakes which when powered with full voltages will cause things to blow up. However, if you have adjustable supplies this offers you the possibility to turn up the voltage from 0 to the target value while keeping an eye on the current drawn. If there is an immediate short or one at a low voltage or the current drawn is higher than expected you will be able to spot that before blowing up parts of the circuit. This can prevent a lot of frustration. I have 2 of this type: MCH-K305D. You can get them cheap at aliexpress and similar sellers. But there are others. A regulated power supply is a thing you buy for life, so it does not hurt that much if it costs a bit of money.

B.t.w. do not focus too much on +12 and -12 Volts. There are a lot of 9 Volt circuits around (especially effect pedals) that can be interesting additions to your musical instruments.