Set the Gen 2 console up with AC adapter plugged in and RF unit attached to TV. Slide Gen 2's side connector snugly into SCD2 and plug in AC adapter at the back of the SCD2 into wall socket.
Power SCD2 by turning on Gen 2 without a game in the Gen 2 console.
Let me clarify, I don't know if you can use the NES ac adapter, but you need a Gen 2 style AC adapter for the Gen 2, and a Gen 1 style AC adapter for the SCD2.