Mate's Dell Laptop (oldish) has flat batt and won;t boot.

Plug in to mains charger - won;t charge - batt light on lappy "winks"
once per insertion of the jack, then nought.

Lappy won't boot either when plugged in to the charger...?

Had batt out & makes no difference except the batt light "wink"
disappears when you shove the jack in.

Got charger here now, plugged in, green LED on tranny box is lit,
multimeter on the DC jack end - measuring 0.01V - it's rated on the
tranny label at 19.5v 3.3A....

Seems something not right - but :-

do laptop chargers "sense" and adjust their output somehow?? meaning I
can't actually say 100% it's the charger that's shagged & just acquire
a new one...?

All help appreciated

Cheers
Jim K