Hi,
Confusing informations...
* You ask about a power supply circuit, but show a measurement circuit
* you talk about 12V supply
* then you talk about a 24V relay... Where is it powered from?
* then you talk about 5V supply..
* then you talk about 500mA for microcontroller and LED ... I'd expect only 1/20 of the given current.
--> please give clear specifications and schematics, even hand drawn is O.K.
5V x 500mA gives 2.5W --> for this high power a capacitive supply is not useful. It is useful maybe up to a couple of 100mW.
Klaus