It may be difficult to analyze this without first finding the errors in the diagram. I believe that:
- the package of the 7912 is not identified so it is hard to know if the pinout is correct, however, I think it is incorrect when comparing to the TO-220 version of the this part. I think the intention was that pin 2 be the GND pin, that pin 3 be the INPUT and pin 1 the OUTPUt
- there is no load or output identified which would greatly help identify the purpose of the circuit. As it is shown, the only purpose appears to be to drain some current from the 25VDC supply and perhaps generate a tiny bit of heat.
Some other puzzling things......since there is not enough DC bias voltage to cause both linear regulators to work in their intended way, then either only one of them is holding its output voltage at its rated value, or neither of them is and they are just acting as resistors. The quiescent bias current (through the grnd terminal) of the 7812 is not the same as that of the 7912, so the 7812 will be starved for bias current and not be able to function correctly.
I am confused by this circuit and find that in addition to being poorly drawn (lacking complete part numbers, missing value of R, puzzling symbol for R, incorrect pinouts) that it is either clever for the sake of cleverness (and beyond my understanding) or, more likely, complete nonsense.