How to Troubleshoot a No Power Issue on your Dell latitude 7390 2-in-1 Notebook?

The first thing to do is to check the power coming into the system. There are three main methods of powering a notebook system. They are:

The Dell latitude 7390 2-in-1 battery :
This fits either to the bottom of the chassis or is secured internally, and charge's whenever the system is connected to mains power. It discharges when no other power source is available but is finite in that once discharged it is of no further use unless charged again. Most batteries have a status LED that advises if it is charged.
There is a subset of batteries we need to cover. On certain systems, you can purchase a secondary battery. These are batteries that are usually fitted in cages in the media bay of the notebook system and are there to extend the time possible off mains power.

original Dell latitude 7390 2-in-1 battery

The Dell latitude 7390 2-in-1 Power Adapter:

This is the external power supply that has one end that plugs to your power socket and another that plugs to the DC connector on your system. These come in one piece for smaller systems such as tablets and come in two pieces for larger notebooks. One side is the power cord that plugs to the electrical outlet and the other is the adapter and plugs to your system. There is usually a power status LED either on the main part of the adapter or as a light ring around the DC connector that plugs to your system.
If the issues appear to be related to either of these, please see our article AC Adapter Not Powering on the Computer or Charging the Battery for further guidance.

The Docking Station:
This is a port replicator device that plugs to mains power with a power cord and the notebook system plugs to it through a docking connector on the bottom of the chassis. The power light on the dock indicates it is receiving power, and the Power button on the dock should light up when the system is docked.
There is a subset of docks that connect through USB or wirelessly, but for this guide we are only talking about the ones with the propriety docking port that connects directly to the notebook.
Does the Notebook require a spacer for the dock (E7x40, E5x40, E7x50, E5x50 series)? If a spacer is not being used for these models, it is possible to damage the docking connector on the system or the dock.

Source from https://www.dell.com/support/article/SLN155074/en