The most important thing to remember when you "emergency charge" at an unknown/unverified source (friend, restaurant, business) is that if your adaptor is not properly grounded it will not work. The light comes on but it's not green but amber or whatever color.
The second thing is heat. I have seen all sorts of disasters in people's garages and mostly with outdoor GFCI receptacles. Remember that when you plug-in you are betting the well being of your adaptor on their good housekeeping habits.
If the receptacle is badly wired the possibility that it will melt your molded plug is high.
So having a heavy duty 1-2 ft cord that you TRUST on hand is a good idea even if you don't need extension. The cost outweighs having to replace your adaptor's plug.
Final advice: if you will truly emergency charge chances are you will use whatever is on hand. Use the shortest and beefiest extension cord possible. Once you get it to work don't walk away!. KEEP CHECKING the plug and extension cord periodically for excessive heat. "Jiggle" connections and ensure there is no sparking sound or flame. It is also possible that the breaker can trip while you sit for a beer in the kitchen waiting for your vehicle to charge.