So, having stood the two electrolytic capacitors up… I see a bit more detail that was hidden beneath them.
I have no idea what the transformer ratio is, but I don't see any regulation on this power supply. There's a full-wave bridge rectifier (D1, D2, D3 and D4), then it goes into C36 which is that monstrous 2.2mF (25V) capacitor. The two extra pins next to the audio input are power outputs, as suspected.
In the above photo, the index mark of the main IC is the top-left. If you look closely, you can identify the various GPIO pins are not connected:
Making use of those will require either very careful soldering, or liberating the part from the board.