Govia Thameslink Railway and leasing company Porterbrook have begun a £55m five-year programme to modernise 214 Bombardier Transportation Class 377 Electrostar electric multiple-units operated on Southern services, and 56 similar Class 387 units used on Gatwick Express and Great Northern services...
To be undertaken at GTR’s Selhurst depot, Project Aurora will include the installation of real-time passenger information screens, USB and power points, energy-saving LED lighting, passenger counting equipment and on-board diagnostic systems including an upgraded on-train data recorder. Forward-facing CCTV cameras will help GTR and Network Rail investigate incidents that cause delays. The first modernised EMU is expected to be completed this autumn, with one unit per week to be completed once the programme is fully underway.
Quotes from RailBusiness: here
The 387s already have power sockets but not USB sockets, but presumably the 377s don't? I've not been on one in ages.