In theory if the both transformers are identical and do not include fancy electronics (regulator etc.)
you may be able to connect them in parallel. If the transformers are identical, the load should
be divided quite evenly with them. If they are not identical, one of the transformers will
take more load and be overloaded. When it fails, all the loads will be on second
transformer that will fail very quickly...
So generally wiring two transformer with DC outputs in parallel is not a good idea.
In some special cases where everything is correct it might work.
Wiring two AC output transformers that plug to wall outlet together is a very bad idea.
If you remove one from the wall and leave other connected to wall, you will have
lethal (almost full mains voltage) accessible on the pins of the mains transformer
not connected to wall!