...It's got something to do with the transformer....
That's what I'm thinking. How are the four ends of that bracket anchored to the studs?
I've seen transformers wall-mounted before, but all of them used verticle pieces of strut bolted to the studs to distribute the weight beyond just a couple of small anchor points. The verticle members also strengthen the bracket as a whole.
Even better than that is to attach the verticle strut to some horizontal pieces so that the weight is uniformly distributed across more than two studs.
-John