There is information on ba.com on the at seat power supply specifications and the use of electronic equipment on board at
https://ukprepin.custhelp.com/cgi-bi...hp?p_faqid=271
and
https://ukprepin.custhelp.com/cgi-bi...p?p_faqid=1335
However, the first of these pages is out of date. As stated in the posts above the latest Club World seats have US and European sockets supplying 110 V AC. First still has the 15 V DC power outlet and requires a DC to 110 V AC Inverter such as the one made by Teleadapt. It used to be possible to borrow a Teleadapt adaptor during the flight on BA provided you were travelling in First. I'm not sure if that is still the case.