Charging sockets were present in Some SL coaches (In my journey, S3-S4-S5-S6-S7-S8 coaches) had Charging sockets near every seat. Rest all SL coaches had two charging sockets each near the Door.
But do keep in mind, the charging sockets near the seats were of 500mA rating. So do check out before using your Mobile charger.
Many people were suffering problem due to Higher Ampere Rating of their Mobile Chargers. And using laptop charger in these sockets is not possible.