I’ve never seen any compact usb adapter with built in surge suppressor, or an in line 5V protector, I would just rely on several surge protectors plugged in at different locations in the house (cameras doesn’t have to be connected directly). If you are familiar with electrical you could install MOVs at the breaker panel, or if you’re good at soldering, you could install NTE4900s in the usb cable or in the camera (voiding the warranty), would you like to sell the dead cameras to me? I’d like to take them apart and try to figure out what failed.