Most planes (certainly all the long-haul ones I've been on) have both a socket that can take what looks like a variety of plugs and they also have USB plugs for phones and ipads etc - at each seat. I'm sure there are a few older planes that don't have them but I'd say the majority do. I learned from experience that my laptop required too much power and the socket switched itself off and wouldn't charge it but that just seems to be a poor choice of laptop by me - so I switched to an ipad and downloadable Netflix