I'm somewhat interested in finding out what pseudo-science explanation they finagle for how the power went out and how the amulets work. I would hand-wave a guess about an EMP or something like that frying all computer chips in existence except for some extra special ones contained in the amulets. But even then people should have been able to steampunk or wind/solar their way to a power source. Batteries and thermoelectrics should still work. Unless the actual laws of physics went crazy. But....combustion still works. So maybe it's just "A wizard/alien did it."