I've recently build a simple bipolar power supply circuit for refresh start. LM7812 for positive power regulator and KA7912 for negative power regulator.
Before I ensured that is OK for output voltage is about 12 volt before attached KA7912 in circuit boards. I've attach ground connect from ground pin of KA7912 to ground pin of LM7812. When tested with multimeter it show me as "20.2 volt" . Can anyone me guide me how can i correct it back to become 12 volts.
Have you noticed the pin layout are different for 7912?
78XX and 79XX have high leakage current and need a little load (5-10 kohms) to show correct voltage.
Do you also have decoupling capacitors on in- and output?
Pelle
The other thing to note is what you are driving them from. They need to be voltage sources that float with respect to each other. What have you got?
That or a bridge rectifier from a centre-tapped secondary (centre-tap = circuit ground).
Show us the circuit!
Wow, a manic depressive power supply 
Sorry, it was too good to overlook.