Using a TL071 operational amplifier can be made a very simple symmetrical power supply. The symmetrical voltage source may be used if the consumer requires a very low current of the order of several mA.
In the diagram below, the upper half provide positive supply voltage. A zener diode serves as a reference of 3.3 V connected to the noninverting input (+) of IC1. To ensure circuit function, the diode is fed through R1 initially and then, when the output voltage is huge enough, through D1. A fraction of the output voltage is brought back to the inverting input (-) of IC1 through P1. The smaller the voltage response, the greater will be the output voltage. Voltage of the operational amplifier can be up to 36V, so the maximum output voltage will be approximately 30V.