Sort of solved.
My laptop, Dell Latitude C840, suffered vibrations for several blocks, including a brick alley. It survived. The power adapter was good for a day. The next day it usually was good. The day after that it sometimes was good. Its own LED was steadily on but power wasn't arriving at the laptop most of the time. Then the LED went out (it has a delay) and, I think, on again.
Then it smoked. It was in my hand, so I unplugged the AC end fast. I think the smoke was from where the PC cable was attached to the brick. And, by the way, the same cable at the PC end was baring wire, and my electrical tape kept sliding off. I don't use the laptop's carrying case; it's too bulky.
Shopping for a native replacement adapter at Dell, I saw a bunch of customer complaints on the same issue. It lasts about a year and a half (the warranty is for a year) for some customers. The adapter is Dell part 310-1093, manufacturer part 3K360.
So I bought OEM for under half Dell's price, located via Froogle.com. To protect the PC-side cable ends, I looked for hard protectors, one so the PC cable doesn't get bent at the brick (the stress reliever is not strong enough, I guess) and the other so the distal connector's wire doesn't bend when I carry this thing around the city. Meanwhile, I'm using a cardboard box. I don't know if anyone makes protectors like I imagine.
And the old adapter will likely land in the trash after I scavenge its cables and maybe break it open out of curiosity. I assume it's too dangerous to plug in again.