Dell Precision 330 - Manual (Page 56)

Removing the Power Supply (Mini Tower Chassis)
1. Rotate the power supply away from the system board.
2. Disconnect the power supply cables from all drives.
3. Disconnect the power supply cables from the system board.
4. Lift the front of the power supply up to its fully extended position.
5. Rotate the right side of the power supply up and away from the chassis.
The pivot pin on the right rear of the power supply rises up and exits the chassis slot.
6. Disengage the retention arm pin on the left side of the power supply from the retention arm socket.
7. Disengage the pivot pin on the left rear of the power supply from the chassis socket.
Removing the Power Supply (Mini Tower Chassis)