It might be an odd old coach (pre 2007 era), but these days railways fix charging sockets to old coaches too.
Attached are the pics of Jnaneshwari Deluxe & Samarsata SF Express's Sleeper coaches with charging sockets!
Pic 01 : Coach made in year 2013
Pic 02 : Coach made in year 2011
Pic...
more... 03 : Coach made in year 1997