It's been very inconsistent for me on 737-800s; on some planes it works fine, others it doesn't work at all, others I need to constantly fidget with it to keep power supply going.

Given that it works on about half the flights, I figure it's not a problem with my laptop, but more of a problem with the source itself - I tend to just mention it to the crew, asking them to put it in the log for when maintenance can take a look at it downline when there's a chance.