You can think of them as either variable resistors, or back to back Zener diodes.
They are ceramic based devices (metal oxide varistor), no gaps. There's no 100% protection.
I highly recommend the Tripp Lite filtered power strips. None of my own equipment has ever failed
since I've been using them.
since I've been using them.
They use MOV and safety capacitors, as well as LC filters. I don't open up the Tripp Lites, though.
Here's an ad with a board photo of one of their 4 socket models.
https://blog.tripplite.com/what-are-surge-protector-joules-and-how-many-do-i-need
