With the implementation of EFB, there are many, many validations that take place before the airline can put them into use. With each airframe, there is significant testing to see if the use on the flghtdeck interferes with any of the electronics or systems. With this testing, there can be certain requirements necessary to protect the systems. These will vary between airfames and even between same variants, depending on the combination of equipage. Most of the time, it is the charger that is the problem, so there are special outlets that shield the flightdeck from interference if there is any.