What would happen if the 3.3V and 5V outputs hypothetically soldered together?

This is more of a question of curiosity I thought of while pursuing another problem. Would the 3.3V regulator struggle until it eventually burned out?

athoesen:
This is more of a question of curiosity I thought of while pursuing another problem. Would the 3.3V regulator struggle until it eventually burned out?

The regulator would probably be unharmed. All the electronics that run off 3V3 would be fried, unless you are VERY lucky.

What if 5V was within their operating range? Would they theoretically simply just... keep working? Or are you saying that it would pull an inordinate amount of current?

Anything could happen.

Depends on which Arduino you want to torture.
The 3.3volt supply pin on an Uno/Mega isn't used for anything else, so if wouldn't make a difference if the 3.3volt supply would burn out or not.
On a Nano, 3.3volt comes from the USB<>Serial chip, and that chip could fry from 5volt.
A Due and newer MKR processors run on 3.3volt, so the 3.3volt pin is the power pin for everything.
5volt there will almost certainly fry the whole board.
Leo..

Athoesen,

I think you think that the regulator can some how try to bring 5V applied to its output down to 3V3, this is not the case. There is an input and an output for good reason. It won't try to regulate over voltage applied to its output, most likely it will just ignore it.