Top camp has no mains 230V electricity.
Top camp does have solar-powered car batteries, so you need to bring a 12V car-type charger for your caving light and phones.
At top camp there is one USB-charging socket (a pair of USB sockets) provided. This just plugs into one of the 12V sockets. Since this is not enough for everyone's phones, you need to bring your own 12V-to-USB plug-in. (Providing proper permanently-wired USB charging is on our to-do list.)
USB to multiple-USB (e.g. 1:4) expander boxes don't work for charging lights. Even for charging phones they are very, very slow. So if you are using USB to charge your caving light you must bring a light charger which plugs directly into the 12V socket.
Base camp has mains power and UK-style 230V mains sockets as well as EU-style mains sockets. So your usual UK chargers will work and you don't need to bring any converter plugs.
We have no permanent USB charging sockets. People bring their own mains-to-USB chargers so you may be able to borrow one, but this does mean that enough people bring one. So to be sure, bring your own (and label it with your gear tape).