thanks, willy, but i'm back to normal - sort of

very puzzled though

background story:
back in the summer i ended up with a windows 10 hand-me-down laptop from my son (originally my birthday present to him

). he claimed the video card must be going bad because the display would occasionally be distorted. anyhow, i played with the power settings and had no problems since last year september. fast forward to february - battery was no longer taking a charge and while i keep the laptop plugged in i ordered a new dell battery to have protection in case of a power failure. that battery showed a run time of 80 minutes or about half what i thought it should be; the seller agreed and sent a replacement. well, the new battery did not do any better.
then i had the glorious idea to let windows 10 choose the best setting for battery life and performance! with that the horror began - every few minutes the display would contract from right to left and then fix itself after 15 or so seconds before it started all over again! through trial and error i found my previous power settings and once i chose 'best performance' the problem stopped. at least, while plugged in! running on battery i still get the distortion but i decided a loss of battery life was the lesser evil and after conditioning the battery by fully discharging 3 times it'll stay plugged in from now on.
but i still can't figure out why having windows 10 choose the best settings created such a mess