It depends in which cabin you are travelling:
https://www.klm.com/travel/gb_en/pre...erType=generic
Sometimes it depends on which route, if they have different fit-outs in the fleet. So putting in your flight number/s can help.
You can also use the many web sites that offer detailed information about airlines cabins and facilities. Just search for 777 in seat power (or similar) and many sites will be available.