Dell OptiPlex E1 - Manual (Page 43)

System Power-Supply Removal (Low-Profile Chassis): Dell™ OptiPlex™ E1 Systems
To remove the system power supply, follow these steps:
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 it toward the back of the chassis, and
hook the tabs into the right side of the power supply.
WARNING: The voltage selection switch, located on the back of the power supply assembly, must be set to the correct operating voltage (115
or 230 V) before the power cable is plugged into an electrical outlet.