Dell OptiPlex Gxi - Manual (Page 118)

System Power-Supply Removal (Low-Profile Chassis): OptiPlex GXi
1. Disconnect the AC power cable from the back of the power supply.
2. Disconnect the DC power cables from the system board and the drives.
3. Remove the power-supply mounting screw at the back of the chassis.
4. Slide the system power supply forward until it stops; then lift it from the chassis.
When you replace the system power supply, place it down inside the chassis and against the right side of the chassis. Then slide the system power supply toward the
back of the chassis, and hook the tab on the side of the chassis into the right side of the power supply.