Ramp Agent reported ground damage to an aircraft due to a malfunctioning belt loader. Maintenance was notified.

Narrative

I was positioning a power stow to aft cargo compartment for Aircraft X outbound. I checked the power stow prior to positioning and appeared safe to use. I did my safety stop and approached aft cargo compartment and began to dock power stow. As it was lowering and leveling; the left side of the power stow snake head dropped and before I could raise it up; it pressed into the door sill denting and puncturing the sill. This happened approximately about XA:55. I was the only person involved. As I was docking the Power stow and it was lowering and leveling; the incident occurred.It appears the Snake head tip came out of the track on the left side of the head. I took the power stow off the aircraft and went to retrieve my radio from my gate bag to call a manager to the gate. I called the manager on the phone after he responded to me on the radio. The manager arrived about 15 minutes after the incident. I tagged the Power stow out of service and called automotive on the radio about the Power stow aircraft incident.