This plugin manages a combo LED button. If the printer is offline, it turns it on (using PSU Control). If the printer is online, but not printing, it sets the extruder to preheat. If the printer is printing, it cancels the print.
Install via the bundled Plugin Manager or manually using this URL:
https://github.com/lbernstone/OctoPrint-Dtrtbutton/archive/master.zip