Have access to a meter? If yes, then plugging in the AC adapter alone, place meter at laptop connector end and find the voltage, is it correct?
If it that is correct, then how old is your battery? If your laptop is 18mos. or older expect some battery issue. Also, do you recall any tripping on the AC adapter power cord? It's possible either the adapter harness is wonky or the connection at laptop is loose or wonky too. Next, no matter what the cause, unless you're willing to break down the laptop to check and inspect innards for obvious damage. If this is an old laptop it may have seen better days. During breakdown, inspect for any dust build-up to include if fans present they work. replace the heatsink compound at cpu while you're open to such.
What does the support website offer from PB. If it is that old, then maybe the bios battery is weak or simply replace upon breakdown. Also laptops that are in constant "heat stress" mode breakdown due to the components failing or can't handle it no more. It has found a weak link, and becomes kaput. Look into all this and see where it leads.