That's only with select airlines and only on long haul flights between major hubs. It's not a feature you can rely on in the least.

Is this a first/business class thing? I've never been on a plane with USB power outlets (though it has been about 6 months since I few last).

Fly on long haul flights, especially internationally with screens on the back of the seats. There is usually USB slots right below it.

I am based in europe and my experience is basically on international flights. Maybe it doesn't apply in the USA.

The flights that didn't have USB outlets were shorter anyway, so the battery would hold.

I've flown hundreds of times in my life and never been on a plane which had power or usb sockets. Airbus 320/Boeing 737 don't tend to be equipped with them.

Sorry, but that's just impossible, really. Any sufficiently long flight, especially international, ALWAYS has power connectors and/or USB slots. Admittedly the power plug is often hard to find, hidden under the seat or armrest, but the USB slots are usually right below the heads up screen for movies. Unless you're flying extremely short distances only, power is basically included in all flights at this point. This applies to coach as well.

Ok,let's have a game. Take any European flight with Ryanair, Easyjet or Jet2.com. If you find yourself on a plane with USB or power outlets,I will happily refund your flight in entirety. Like I said,I have flown hundreds of times(20-30 times a year for about 5 years), only with those airlines, all flights were about 2-3 hours long, and not a single one of them had USB/power sockets.

I've flown from LA to Boston, New York several times over the last year and I don't recall a single USB or power cord outlet.

On every international flight I've taken, there has been USB power but zero power outlets in coach.

You're definitely not looking hard enough then. Like I said, they are typically hiding somewhere under the seats. There is NO WAY a super common flight like LA to NY does not have power.

Mind sourcing that? I have also have not had this experience.

I'm on a plane at least once a month with Delta and American Airlines and even small regional jets tend to have USB plugs or power outlets. It may be hidden under the seat or in the arm rest, but what they're saying is true. Most if not all airplanes have power available.