Option two has the advantage of maintaining a healthier life-work balance, but it also relies on there being an empty seat in First. I have used both the second and third options above, which both work.

Travel with the long power cord, and connect that to the brick and plug it into the recessed socket.

use the 3 pin UK plug on the power brick, and attach it to an adaptor for the US 2-pin style - if your adaptor is a standard size, it's likely to fit into the recessed socket).

Bring an international travel adaptor with you (e.g. When youre the queen of the holidays, you get more than a meal.

Ask if you can charge the MacBook in First, and watch a movie at your regular Business seat while it charges.

Upgrade to First - the power socket is not recessed.

The problem is that the socket is recessed in the console, and even the smaller power brick for the MacBook Air won't fit (you can insert the pins, but not far enough). However, United Business have new lie-flat seats, with a new 110V power supply instead of the old airplane-style one. And I fly United because of their generous air miles packages which make upgrading affordable. I fly often and have to upgrade to Business so as to ensure a power socket at the seat. Not sure this is a hint, more a warning and how to get around it.

United airline app mac