Atari 2600 AC adapters are not particularly reliable. This new 1/8" mono DC plug can be soldered to any DC adapter rated at 9V and 500ma (or higher) to create a functional power supply compatible with many 70's era game systems.
Atari Pong systems (various)
Coleco Telstar sytems (various)
Magnavox Odyssey pong systems
Numerous 70's era pong systems with built-in 1/8" (3.5mm) mono-style DC jack.