Well, turning the plug upside down didn’t permanently solve the problem — the lines came back even worse than before. A few days later, the GFCI outlet in the kitchen I was using died after a long air popper popcorn session (circuit overheating?). Maybe a coincidence, but after I replaced the old GFCI outlet (my echo show was actually one outlet away, but was downstream from the bad/old outlet and on the very same GFCI outlet circuit), my unit no longer had lines! So, perhaps a bad GFCI outlet was creating excessive electrical noise on the circuit? I will report back if my unit stays “fixed” from the new GFCI outlet installation. Since most people use these in the kitchen, and kitchens have GFCI circuits, perhaps this is a common problem?

I had wiggling horizontal lines at the bottom of the screen. I believe it may have been related to the power supply polarity. I plugged the power supply in upside down in the outlet (with the cord end facing up) and the problem when away.