Here is an excerpt from Heald's blog that discusses this.
"A a few people had reported that they needed these for medical reasons to charge appliances like PAP masks for sleep apnea, etc. Well, obviously these are allowed and I have had this confirmed by all the right people in Miami. Their suggestion is where possible to put these in your carry on and where this is not possible to please place them in your suitcase with a note attached to the charger etc that says “USED FOR MEDICAL REASONS.” This may sound a crude way of doing this but it will alert the people who are looking in the suitcases for prohibited items. Obviously, allowing lots of electrical items to be plugged into the ships system is dangerous and can overload it."
Hopefully; "All The Right People" will inform the ship's personnel about this. There is often a disconnect between corporate and the fleet.
OK folks: Here's your chance to make a million dollars. "CORD RUNNERS". Smuggle your extension cord without it being detected.
The first one who brings it to market will make a fortune.