I guess I'm a little confused on what you have there...
Medium and Large Dingbats come with one silver bracket for mounting the first power supply. The first power supply would be mounted between the center rib that acts as the second bracket and the included silver bracket. If yours came with the Mondo mounted, it should have used the included silver bracket.
A second power supply requires two of the silver mounting brackets, one for each side of the Pedal Power and mounts to the second position.
The screws in the sides of the Pedal Power are removed and re-used to mount the brackets to the sides of the Pedal Power. The Pedal Power with attached brackets then mounts to the pedalboard using the included 6-32 flat top screw and keps nut.
Please give us a call directly or write to firstname.lastname@example.org
if you are missing any of these pieces and we will get you what you need.