The Intellivision gets its power through the mains plug.

Intellivision Mains Power In



After that the two black 110/230V AC wires go to the transformers primary coil on the bottom.

Intellivision Primary Coil



The secondary coils out of the transformer then pass through the power switch.

Intellivision Transformer Wiring



Intellivision Secondary Coil Wires



Intellivision Power Switch



The transformer inputs are on the right (blue/green/green) and the switched outputs on the left (white/blue/black).

In short, the mains power comes into the transformer directly on the primary side, the secondary coils (two of them, one is double-tapped) go through the power switch including the reference ground and come into the connector with two sets of 10V AC rails, which feed the 5V and 12V regulated inputs.

Intellivision Transformer Ribbo



The Black/Blue rail feeds the input to the 5V regulator. The White/Yellow rail feeds the input to the 12V regulator, as well as taps off for the unregulated 16V.

Intellivision Transformer Power Rails



Intellivision D Power Ribbon



5V Power Rail

The 5V regulated rail is generated by the Hitachi HA17805P LDO regulator.

Intellivision 5V Regulator



12V Power Rail

The 12V regulated rail is generated by a MC7812CTG (or similar) LDO regulator.

Intellivision 12V Regulator



16V Unregulated Rail

The 16V unregulated rail is tapped off the transformers full bridge rectifier. So is essentially unregulated.

Measuring with multimeters when not loaded down this is typically showing anything up to 24V.

Intellivision 16V Unregulated Rail



-2.2 / -3.3V Rail

The -2.2 / -3.3V negative rail is generated from the diode drops over the secondary coil and smoothed with a few capacitors.

Intellivision -2.2 / -3.3V Rail