The missing information from the OP's description is if other seat sockets were also not receiving power, or if it was just the seat in question.

Once the flight deck is no longer sterile (above 10k feet) then on most aircraft types the flight deck crew need to flick the switch to direct power back to the ports. Sometimes it isn't deactivated, but recently I've seen this occur when they are activated on the ground, off once disconnected from ground power supply (APU) and during taxi and takeoff, then reactivated above 10k feet.

The way to tell in future if it is just your seat or every seat relates to a small green LED light above the socket. If this is off but every other seat socket is on, you have a problem. If all are off, then the supply needs to be flipped on for all seats.