Southwest overall seems to be the best when it comes to getting the airport to put in power for flights. On many of the southwest flights I have been on the waiting area had more comfortable seats (like the ones found in lounges) with power, long tables with power, and power by other seats.
Other airlines in the US want you to pay for the lounge access so they have no particular incentive to partner with the airport to provide more amenities to the non-lounge crowd.
Overall the smaller airports tended to provide more in this regard