NEO-POWER-0
NEO-POWER-0 is an add-on board found in some late first generation home consoles (NEO-AES board).
It was probably added to prevent users from frying their system by using 9V power supplies.
The board itself is a simple step-down converter, allowing to safely use voltages up to 12V.
The circuit was then included as part of later revisions of the main board.
Pinout
Red: 5V out. Yellow: 7.5V to 12V. Black: ground.