Why does my iPhone XS turn off when connected to a charger and turn on when removed?

vishnuvarthan ~ As your iPhone XS is an old model, it's worth checking for a weak, aging battery which can cause various issues. So...

Does your iPhone XS still have its original battery?

And what's the Maximum Capacity % here?...

Settings > Battery > Battery Health & Charging

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This is weird. Are you using original apple charging cable and adapter?

This can happens if there is an issue with the charging port of the iphone or a short in the adapter.

Try to charge the iphone with another cable and an adapter.