Dell OptiPlex E1 - Manual (Page 61)

System Power-Supply Removal (Mini Tower 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 system power supply.
2. Free the system power supply from the securing tab labeled “RELEASE —>,” and rotate it upward until it locks.
Press the securing tab to release the power supply.
3. Disconnect the DC power cables from the system board and the drives.
4. Facing the left side of the computer, move the front end of the system power supply toward you, and lift it up to disengage the power supply from the slot in the
chassis.
5. Lift the system power supply from the computer.
When you reinstall the system power supply, place the power-supply detent link over the pin on the power supply as you position the power supply in the chassis
opening.