Ok, before everyone starts immediately telling me "NO" let me explain. I bought a new house last year and the original owner had installed a brown wall outlet in the garage. Now, there are also 2 brown outlets in the house. They are different than every other outlet in the house and according to the home inspector have no power that goes to them. 1 of the outlets is behind the fridge and the other is in the hall. According to the directions in the garage the brown outlet in the garage is where you plug in a generator and it feeds power to the otherwise "dead" outlets indoors. My problem is how do you plug the generator into the wall outlet? Can you buy a power cord with 2 male ends? Also where would I even go to get it? There is no risk of "backfeeding" because these outlets are not wired into the rest of the home wiring.
You should replace the garage outlet with an inlet, such as this (Amazon, as an example).
This way, you can use a standard male-female cord, either a standard extension cord or one made with the correct gauge of SO cord [Thanks, @EdBeal]. You avoid using a male-male cord which is so dangerous.
I think the reason the owner did this is because if he has a male plug inside, how does he plug an appliance into it? I think he has a double male plug from his generator to an outside dummy socket. Then that socket is connected to an inside dummy socket. It must be for hurricanes in order to not take cords through windows. This is potentially dangerous since you have a male end with power that can touch you when you're handling it or some other conductive material. I wouldn't recommend it. That male socket in the pic would be perfect in this case if its the one outside. No danger since it's a dummy and the only way to power it is to have it covered.The male to male plugs are called widow makers.