There is probably nothing wrong. Some computers including Samsung have a software application which limits the charge to 80% to increaser the life of the battery. Look in the Samsung programs menu and you will probably find it there where it can be disabled if you wish. Personally I only disable it on the odd occasions when I know I might need a longer battery life then I switch it back on.
The Legend of Zelda Breath of the Wild review: Five hours with Zelda on the Nintendo Switch