I've been on 6 flight segments in the past three days (and about 15 since I got my MacBook). More often than not (~90% of the time) I have been unable to charge my MacBook from the in-seat power. This has been on a variety of aircraft, all Boeing. 737, 757, 767, 777. I'm using the stock charger with the USB-C cable. I've tested the outlets with other devices (none of them with a ground plug, BTW) and they work fine. Anybody else experience this?