This is the Luna II (G2) Power Adapter. This is one half of the full power cord. This is the section that attached from the power brick to the device itself.  

This Universal 65 Watt AC Power Supply with Cord is designed for use with all Luna II Series CPAP & BiPAP machines. It includes a North American (US & Canada) AC Power Cord as shown.

USAGE: This Universal Power Supply will automatically adapt to voltages in most countries worldwide. (A plug adapter may be required for use outside of North America.) It is the only power supply that should be used with any Luna II sleep therapy device. Using a non-Luna II power supply with your machine may damage it and void the manufacturer's warranty. For complete instructions review the documentation that came with your equipment.