Although they look the same and fulfill the same purpose, their quality is miles apart!
Extra heavy-duty rated cover can withstand more damage. The hinges are sturdier and the cover is more durable, protecting the outlet inside from the elements. Of course, this also comes with a higher price.
The U.S. NEC Code requirements Sec. 406.9(B)(1) requires outlet covers installed on enclosures and in wet locations to be listed “extra-duty” rated for this very reason. Light duty is still offered for those areas where the code is not enforced, and the contractor is trying to save money.