The power system in coach is connected in to the AVOD system. If the AVOD is working, there should be power. If the AVOD is rebooting or problematic, the power may not work. This was my case on my May SYD trip.
The power is not high wattage. My 15" MacBook Pro did not recharge completely despite being plugged in for hours, but it can probably sustain use and prevent battery drain.