That particular company must supply a LOT of power adapters to various companies and while they are inexpensive, the failure rate is probably a little higher than we'd like to see. I've seen other devices brought down by defective "wall wart" power supplies, so it's not an uncommon problem (and not just for VoIP device manufacturers).
This is one of those cases where you wish Chinese companies would pay a little more attention to quality control, instead of just trying to sell as many units as they can. The problem is that in most cases the end user gets the device indirectly (bundled with something else such as an VoIP device or a router) and therefore it's either the customer or the seller of the bundled package that gets stuck with the bad units.
