External power supply damaged board?

Hi everybody,
just to know, is there any relation with the symptoms and problems described in this post?

Also, if a live connection (while is USB powered) to EXT Supply plug was done, is it possible an spike (if different grounding system is used, current flows balancing), apart from the absolute maximum voltage exceeding, could damage the board (i.e. the more sensitive components in the path)?

Any recommendation to prevent this potential damage risk (i.e. as power up sequencing, power source limitations, no live connection, safe USB removal, etc)?