wrong voltage will have shorted out the connector or fuse inside on the motherboard.
the good news is it should be simple to fix,if it had a fuse then that will need replaced/resoldered.
if not then you'll probably need to resolder the connector. possibly replace the charging circuit.
The bad news is it can be a complete and absoloute bastard to break a laptop down to its motherboard without breaking things (like little plastic clips on the case and such, mainly cosmetic)
as it was working fine on battery power afterwards then it suggests that its just a connector/charge regulator issue and nothing seriously major.
Ive stripped down enough laptops now to know that its generaly less of a headache to take it to a specialist and have them do the job, that way if it all goes tits up you have some kind of warranty.