Hard To Diagnose
The difference between functional and broken Belkin hardware is infinitesimal. I wonder how they noticed this issue. Perhaps large groups of Belkin routers inexplicably started routing traffic properly?
From experience I do know how to tell if a Belkin UPS is working properly. If all the equipment attached to the UPS is on fire and the UPS's transformer is performing a china syndrome then the unit is operating according to specification.
The above little tidbit of knowledge isn't of much use anymore as Belkin stopped manufacturing UPSes after their last factory worker was transferred to the QA department and was promptly electrocuted.