It's not. Your PSU isn't really a 500W. It just says that on the label.
Unfortunately, there's no governing body that will allow us to win a class action lawsuit against people like CiT for selling PSUs that are fire hazards. They can put whatever number they want on the PSU and hide the actual number in a PDF document you have no access to (read Hitcherhiker's Guide to the Galaxy, when they talk about the permit for knocking down Authur Dent's house. It's all true)
If the PSU dies, they're only bound by warranty laws of the country.
If the PSU catches your house on fire, you can take them to court, but their lawyers are more expensive then your lawyers and you'll end up living in the streets.
It sucks. I know.