Unlike standard ATX power supplies that use a green wire for "Power On," the D220P-01 requires a specific signal connection to activate its 12V rails.
Dell D220P-01 (also known as the adapter) is a 216W–220W external power supply used for legacy Dell OptiPlex Ultra Small Form Factor (USFF) PCs. It features a proprietary 8-pin connector that provides a steady 12V output at 18A. 8-Pin Connector Pinout The pinout below describes the female receptacle Dell D220p 01 Power Supply Pinout 2
It was a Dell D220P-00, a heavy, beige brick of a power supply from an era when computers were built like tanks and sounded like jet engines. Understanding the Dell D220p 01 Power Supply Pinout: