How to use Zener Diode in Parallel RC circuit
No Zener diodes need to be abused:



When V1 is present, it will supply current for R1, R2, and charge cap C1.

When V1 is disconnected, the cap will supply current to R2 but not R1.  Of course the energy in the cap is limited, and the voltage across R2 will decay exponentially towards zero over time.

There will also be a voltage drop across the diode, even when it is forward biased.  For example, if V1 is 10 V, then there might only be 9.6 V or so across R2, depending on the current.  If this is not acceptable, then a more complicated topology that switches a FET is needed.