(Solved) Video hardware acceleration stopped after upgrading (It was the power adapter!)

[LC2016]

I posted last year that after I upgraded Chrome on Linux Mint 18, my laptop ran much slower... most of the time. Sometimes it didn't, but I didn't connect the dots until one time I accidentally left my power adapter at the office (the Flextronics one my work provided) and had to buy an Insignia power adapter from an electronics/appliance store. After that I never had the slowdown when working at home, but when I returned to the office the slowdown recurred.

I tried several times in controlled circumstances, and found that if I booted my laptop and logged in while plugged into the Insignia, or not plugged in to any adapter, or even plugged into the Flextronics but with the Flextronics not plugged into mains power, then there is no slowdown. If I boot the laptop while plugged into the Flextronics while on mains power, then there is a slowdown the entire time until I shutdown.

I don't know why the Flextronics didn't slow down the computer the first 7 years, but maybe the Chrome update is a red herring. I still don't know how a power adapter can slow down the computer, and not having the computer on any power doesn't slow it down.