HP DL120 - Manual (Page 71)

Removal and replacement procedures 71
3. Remove the default power supply unit.
Reuse the three screws you removed in this step for installing the new PSU.
a. Remove the two PSU screws on the rear panel (1).
b. Remove the single PSU screw on the side of the chassis (2).
c. Lift up the PSU from the chassis (3).
4. Install the new power supply unit.
a. Lay down the new unit in the PSU section of the chassis (1).
b. Insert the two PSU rear panel screws (2).
c. Insert the one PSU screw on the side chassis (3).