Thank you ALL for the replies.
So if I understand well now,
voltage( current) has this charging path:
mains charger --> the laptop charger circuit --> battery.
So, a question is: How to find out that the reason for NOT charging is the laptop charge circuit fault.
What steps to take to repair the charger circuit ?
I think that a similar voltage path , the same principles, are the same for various devices including cell phones.
From my experience regarding cell phones , I had mobile that indicated charging, yet not charging the battery in fact( only pretending charging).
How it can be then?