I have an Acer Aspire ES1-512 x64-based PC (laptop) with Windows 8.1 6.3.9600 N/A BUILD 9600.  When it is using the battery (not plugged in) it is fine, but recently it began to behave very, very slowly whenever I plugged it in (while charging or NOT charging the battery).  Is there a setting I inadvertently set to make this happen?  Please HELP!  It's running about 10 times more slowly when it's plugged in.  THANK you.
Wild GUESS, but based on a real happenstance.
Your  power mains have a high level of NOISE interference with your laptop.
Or, the charger is going bad and feeds trashy power to the system.
Last thing you might find is  -------  The battery!

Does it run without the battery?

Actually, after I posted I went home and looked at all my settings, and indeed, I finally came across one setting which opted for maximum speed/spare the disk (which minimizes speed).   When using the battery, it opted for maximum speed, but when it was plugged in, it opted for minimum speed.  I reset it and it immediately began to behave properly again.  I have no idea how that happened, I certainly did not do it knowingly.  Someone may have hacked into my system.