I'd just stick to a normal Plug to USB charger. That's just me though.
Not 100% on this second bit but I do know it affects light fixtures, I'm aware that some maintenance voids home insurance if not carried out by a certified electrician, as above, light fixtures are the ones I'm aware of but it would make sense to affect wall sockets too, maybe someone else can confirm.
http://www.amazon.co.uk/TeckNet-Univ...words=usb+plug
Would this not suffice? Can click around to tone the amount of ports down.