Modern Windows settings alters default power plans. Legacy control panel options have power profiles and can have separate settings  Anyways glad its fixed.  Mark this is solution so that others can find it.   
I suspect there might be a simple answer to this but I can't find it... I'm on the Balanced power setting. I've tweaked the power and sleep settings for when the machine's on battery power to this: And when it's plugged in and powered: Yet nothing happens on either power setting: the screen stays on and the machine does not go to sleep. I've checked the setting in Settings > Power & Sleep, and in Control Panel: all set for the same as above. I checked Dell Power Manager in case there's a setting there but there isn't. Is there another setting somewhere that I've missed? Thanks.
XPS 13 9305 ignores power and sleep settings