There is a 4th screw tab on the power supply, but my unit had no screw here. Your experience may differ.

Tilt the power supply out slightly, to clear the bracket at the top, then slowly lift up to remove.

It may help to bend the plastic bottom shell of the projector away, gently, to help free the main AC power socket.

When lifting the power supply out, pay attention to the rear screw tab. It's sharp metal, and is very close to the back of a large PCB. Don't scrape it (or worse, knock small components off)!