Can someone tell me why my Alienware laptop switches between AC power and battery power?

I have an Alienware 17 r3 with an i7 6700HQ and a GTX 970m.  For some reason, the laptop switches back and forth from AC power to battery power.  This seems to happen so far only when I'm playing games and taxing the system a bit.  When I'm not doing demanding tasks, like browsing the web, viewing photos, watching movies or running normal desktop apps like Microsoft Office, it stays on AC power.  I can tell when it's happening because the light around the power button changes from blue to yellow/white and back to blue again.  The display brightness also changes and when it switches to the battery I believe it causes my system to switch from the dedicated graphics card to integrated graphics and then back to the dedicated graphics when it switches back to AC power.  This happens quite frequently, like once every few seconds.   

Any feedback would be much appreciated.  

Additional info: 

- Using a stock AC adapter from Dell that came with the laptop when new.  

- Bios is updated to version 1.3.12 dated 07/28/2017

- Power plan is set to Performance