Well, this was news to me:
… after some troubleshooting, I learned my second lesson of the day: PowerBook and iBook adapters, if left plugged into a wall for too long, might need to actually be reset. This can easily be done by unplugging both of an adapter’s ends for at least 60 seconds.
Apparently David Chartier of The Unofficial Apple Weblog observed the coloured ring on his power adapter tip randomly switching between orange and green. That triggered a call to Apple support where he discovered this tip.
I generally leave both my PowerBooks plugged in at the wall and simply use them on battery when I want to go walkabout with them. I’ve never observed this random colour switching, but I guess it wouldn’t hurt to unplug the adapter from the wall occasionally.