Need to check mounting depth of the UPS, and available space between the front mounting rails and rear of the wall box.
All versions and serial ranges.
The new Short Depth UPS may fit into a small wall box.
The new Short Depth Smart-UPS will not
fit into AR106 or AR109 because there is not enough room to connect power cords into the UPS.
The AR106 and AR109 have about 13" of available mounting depth, as measured from the front mounting rails to the rear of the cabinet.
A UPS would need to have a mounting depth of 11.25" or less to allow room power cords to plug in.
You can also find compatibility to all NetShelter cabinets and APC products by Googling "netshelter accessory compatibility chart" and pulling up FAQ 158651: https://www.apc.com/us/en/faqs/FA158651/