Hey guys I think I've done the same thing my Adifruit motor shield was stacked on the v3 Uno
I by mistake put 12vlts on the wrong terminal block thought because the driver had two motors it used two separate power connections so just connected to anyone lol. After the smoke the Arduino would not communicate correctly and time out uploading library's. So then I thought will that Uno is dead so I grabbed by other one lol put motor Shield on uploaded my library connected my motor put my 12vlts on correct terminal block this time all was good until putting power jumper on more smoke and another dead uno this time Unknown USB device error . I'm guessing my motor shield that seems to be OK is actually not and now frying everything it connects too. Now all my boards are dead is there any way to fix the Uno by replacing the big chip or is she toasted for good