Whenever I've been in F (which has only been on a 744 in the last 5+ years) the crew always have had an Empower kit that they happily loan me to plug in my computer. If it's a busy flight and power is going to be important for me, I've asked as I settle into my seat during boarding, if they could find me one, so that they don't loan them all out before I ask.

More often, I'm in CW, and can simply plug in to the at-seat outlet.

In most cases, it really shouldn't become an problem, but will also be nice when they get the rest of the fleet updated to something more modern!