Hi @babamusah
Here's a [https://www.alisaler.com/dell-15-3467-3567-15341-1-91n85-vegas_turis-skl_kbl-schematic/|link] to a free download for the motherboard schematics that may help.
You will need to have a DMM (digital multimeter) and also know how to read schematic diagrams if this is to help you find the problem.
On p.103/105 (pdf numbering) there's a block diagram of the power supplies in the laptop that may be a good place to start.
On p.44/105 it shows the charging circuitry control IC.
Hopefully this is of some help.