Dell OptiPlex 9020 All In One (Mid 2013) - Manual (Page 29)

4. Remove the screws that secure the PSU to the chassis. Lift the PSU up and remove it from the computer.
Installing the Power Supply Unit
1. Place the power supply unit on the computer.
2. Tighten the screws to secure the power supply unit to the chassis.
3. Thread the cable on the hooks in the computer.
4. Connect the power-supply cables to the connector on the system board.
5. Install:
a) power-supply fan
b) input/output (I/O) board shield
c) system-board shield
d) VESA mount bracket
e) back cover
f) VESA stand
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