Dell OptiPlex 3000 Small Form Factor Service Manual page 68

Steps
1. Disconnect the power-supply cables from the connectors on the system board.
2. Remove the power-supply cables from the routing guides on the chassis.
3. Remove the three screws (M6-32) that secure the power-supply unit to the chassis.
4. Slide and lift the power-supply unit off the chassis.
68 Removing and installing components