I believe you are correct (I work as a pilot). The plugs in the aircraft I fly have a bunch of protections to prevent shorts/overheats or other problems.
Electrical fires on an airplane are very, very serious.
If I am correct you can also charge the new MacBooks via usb-c, along with MagSafe, correct? I would just carry an "airplane" USB-C charger with lower maximum charging specs, you probably can also use it for headphones or other usb-c accessories at your destination as well.
Bonus tip: The plugs get worn out on the seat power sockets, and they usually just let the plugs fall out easily. Passengers don't report them usually, and replacing them is very expensive as well. (Take anything in aviation and triple it because it is going into a certified airplane.)
My hack is to carry a cheap EU or British to US adapter (I live and usually fly in the US) as that portion is hardly used on the aircraft and will still hold the plugs tight when the US slots are worn. They are cheap enough if you lose it or forget it you can get a 2 pack on amazon for $8 as well.