|Parts fail. |
It's as simple as that. Whether your PSU going bad affected the WAN side of the router, or they were separate issues, who knows. Without detailed (time consuming) testing to ascertain exactly what happened, it would be hard to say for sure what went on with your router....and the truth is, nobody is going to spend that kind of time to figure out what happened. For what it costs to replace one, you toss the bad one in the garbage and say, "It's NG" (ng = no good) and replace it.