I'm trying to use a L7912 to output -12 V DC. The datasheet says to use a 2.2 uF tantalum capacitor on the input for stability. Further it says if an aluminum electrolytic cap is used, to have it at least ten times the size. The closest I could find was a 47 uF electrolytic cap. Without the cap the regulator works fine. If I put the cap in, (C2, + at the ground side, because it's negative voltage) the regulator seems to let the unregulated voltage through (higher, ripply).
What am I doing wrong?