I have 'dim display when idle' turned on for battery, off for AC.
My laptop had been idle on battery for a while, with the display
dimmed. I plugged in the power supply before pressing any keys. The
display remained dim, even after I pressed a key; I had to turn it
back up manually.
What should have happened: plugging in ac should have restored the brightness.
One additional failure mode:
I have 'dim display when idle' turned on for battery, off for AC.
My laptop had been idle on battery for a while, with the display
dimmed. I plugged in the power supply before pressing any keys. The
display remained dim, even after I pressed a key; I had to turn it
back up manually.
What should have happened: plugging in ac should have restored the brightness.