Hi @faintflicker welcome to this user to user discussion forum. This is not Dell Support. 

All the Alienware m15 laptops have Hybrid Power Design. The design intent of Hybrid Power is to allow the Alienware m15 systems to maintain full system performance under extreme heavy loading conditions. Hybrid Power will draw power from both ac adapter and battery. Without hybrid design, when the system power needs more than just ac adapter power, then the system will throttle due to lack of power. With hybrid design, it prevents system throttling, by drawing more power from the battery to support additional power needs by the system. Battery capacity will drop during heavy loading. When the battery capacity is low, then system throttling can be encountered.  

Please click on Kudos to say thank you for response from user that is not employed by Dell. Please share an update on progress, so that other users derive benefit from your experience. Thank you. 

Not sure if that applies, as my laptop was plugged into a wall socket. Does the hybrid system kick in even when the PC is plugged in?

You'll be able to tell when it's in operation because the alien head start button will flash while it's charging. And, you can get a status by hovering the mouse over the battery icon in the tray. Happens all the time for me when I'm playing MSFS 2020.

Thank you. I will check on this tonight.