Windows 10 Mobile running smartphone switch on automatically while plugged-in. This behavior can be undesirable at times especially when you want to leave your phone alone and switched-off and don’t want to take a call or text and still want it to get charged. Now, if you want to change this behavior and you are one of those who are fine with mods and hacks on your device you can use WPTweaker, a tool originally designed for WP8.1, that can be used with windows 10 Mobile devices to enable it.
Check the screenshot below that gives an idea about the toggle to change this behavior and above image shows Lumia 1520 charging while in switched-off condition. It works on other devices too as per the XDA thread.
You can download and install WPTweaker from here. But remember you will do it at your own risk.
Thanks Raghu for the tip. Cheers!!