why cant we use internal power port and external barrel connector simultaneously. i just want the explanation.
it depends of schematic of your internal and external PSUs. If you apply external power source to output of internal PSU (or internal power source to output of external PSU), it can damage one of these, even if it not powered on with 220v
You need smart circuit to switch between 2 PSU, or mechanical switch to manually select (manually switching) internal or external PSU
It looks like PSU for 110v or 220v. It can be with manual switch or automatically detects input voltage