[arch-general] Blank screen after an interval; maybe related to laptop power supply?

I turn on my laptop, sign in (Linux getty), and use the laptop for a couple minutes (no graphical applications), then the screen goes black and the machine does not appear to respond to any user input (CTRL+ALT+F2, etc.). The only recovery I have found is to hold the power button and restart. The logs show nothing. When I use the computer without the power supply plugged in, the problem doesn't manifest. I'm using a Dell Precision M 4700. Any suggestions? What should I be looking at to begin diagnosing the problem?