Plantronics S12 has two different sized A/C transformer plug-ins

The New S12 A/C transformer plug is slightly larger and has “500mA” typed above the plug.

The new S12 uses 45671-01: https://www.headsetsdirect.com/45671-01-ac-adapter.html

The old S12 uses 73079-01: https://www.headsetsdirect.com/73079-01-a-c-adapter-s12.html