Steve,
I'm pretty sure the problem is not "A spurious signal from defective power supplies". My Surface Book shows this problem on pure DC power from the (huge) batteries in my off-grid house.
If it sees 15 Volts like Microsoft's 65 Watt power brick provides, the charging circuit can keep up with most CPU loads, and only rarely switches among batteries "charging" or "fully charged" or "in use". If the Surface batteries are really low, it seems easier for the system to show them as "charging" consistently. As the supply voltage drops or the CPU load increases or the Surface batteries get almost full, the state transitions get more frequent.
Right now, if I open the battery display and leave my mouse stationary, both batteries show "fully charged" constantly. Mouse over the tray icon for a minimized Explorer window and it hits one of the batteries. Wait for both to return to "fully charged", and mouse over the icon for Firefox - it hits both batteries. Position the pointer over a taskbar icon, wait for "fully charged", and then move the mouse to show the preview - the sudden CPU load hits both batteries and closes the preview!
The real problem here is that changes in charging state hide the taskbar previews. This has been happening since Win 7 came out, on many brands of notebook with totally different power bricks and charging voltages. Microsoft chose to blame the other vendors, and never fixed the real problem.
Since it seems they are unwilling or unable to fix the real problem, providing a 15 Volt power supply to affected users would be Microsoft's quickest way to reduce (but not eliminate) the appearance of the problem. I wish you luck with that! But I'm pretty sure all you need as data is whether a user has the 12 Volt or 15 Volt supply. Any 12 Volt supply (at least in my experience) will trigger lots of disappearing taskbar previews.
Loren