Have you tested voltages around with a multimeter (be careful with live wires of course)? What is your line voltage coming out of the socket? What is the output voltage coming out of the power supply? It could be overvoltage burning electronics inside the router.
Also, power surge can be another possibility. Verizon-branded power strips used in installation, as clearly indicated on itself, do not provide surge protection. I recommend for you to buy an UPS for backup power, power surge, overvoltage, and undervoltage protection.
I hope this is helpful.