We took 2 with us in hand luggage no problem.
Now with My Disney Experience, Wifi in parks plus being able to use our UK phones over there at no extra charge we used the external power almost every day.
We take all electrical items in hand luggage never had a problem but I have been moaned at my US security for carrying an excess amount for a vacation. He said "I hope your plane is not leaving soon as I am going to be a while checking all this" I started being a bit clever and said "no you have about 4 hours before we leave" but I realised he could get awkward so I shut up.

Last weekend was a struggle, only had 5kg pp with Thomas Cook. I usually have about 12kg. Had to spread it between 3 of us.
they give you trouble about your electronics?
at domestic security?
i carry a lot of stuff and no one's ever said a word....
but they're so inconsistent...
on one trip, i flew out of detroit airport twice...
the first time, i was connecting on my way to orlando....(in other words, i'd flown in from overseas, gone through immigration etc, and then had to go through security again for my domestic flight to orlando)..
so the detroit TSA woman insisted that i take off my "jacket". But it wasn't a jacket.
It was a shirt that i had on with a flimsy tank top under it. The top shirt was not meant to be taken off (and the shirt underneath was definitely not to be seen on its own)..
i tried to explain, but there was no explaining.
so i gave in and took off the damn shirt and walked looking like s**t through the sensor. i mean geez. i should have been arrested for indecent exposure.
a few weeks later, i flew back through detroit. And again, had to go through security in Detroit.
I was wearing the same outer shirt, but this time i wore something a bit less revealing underneath, so that i could take the top shirt off at security (which i did on my own in orlando).
so at detroit security i started taking off the top shirt and the TSA woman - a different woman - said to me, "you don't have to take that off, it's just a shirt, not a jacket".
So i said, "but they made me take it off here two weeks ago".
to which the TSA woman responded with vehemence "well that's just stupid!!!" (and she said it with a great deal of disdain in her tone of voice)
so the same shirt.
the same TSA position.
just two different TSA people, though both women.
with two completely different outcomes.