C64:
Pin 1: GND
PIn 2: GND
Pin 3: GND
Pin 4: Not connected
Pin 5: +5v
Pin 6: +9v
Pin 7: +9v
C128:
Pin 1: +5v
Pin 2: Not connected
Pin 3: +9v
Pin 4: GND
Pin 5: +9v
Connectors are different of course, but that aside, they are very similar. I don't see why it shouldn't work.
[EDIT: Wait, hold that, I read it the wrong way around. I thought you said 128 PSU to power a C64]
