Airline power adapters are useless on most domestic flights on the majors, as they don't have any power points. Not even in First.
On most international-class aircraft (all widebodies, I-class 757's, etc.) it's still mostly a wash if you're flying a US-flagged carrier - they have standard 3-prong 110 outlets. Just use your brick.
Check NWA's website, they should have information about what they provide.