I had something like this with a MacBook Pro some time ago. It's probably worth replacing your charger to see if that does the trick. In my case, despite the dramatic "phut!" and black on both socket and connector, it was only the connector/charger which had gone. It seems a bit hit and miss with third party chargers. Perhaps someone can recommend a good source of reliable ones... Keeping a PowerBook G4 going here too. It's a lovely computer and does a few jobs well.
No luck catching it so far. It hasn't appeared in a picture yet, but it's similar to the effect in this photo, taken with a Sony compact (that camera is fine, but I had a problem with transferring RAW files to iPhoto. I don't think my camera is supported)