It's not "illegal" unless hardwired that way. You can plug in any size or type of portable equipment downstream from the outlet. You do it all the time at home, e.g. plug an 18 or 16 gauge power cord into a 15A-rated outlet on a 15A-protected circuit. For example, a table lamp or a crock pot. It is not required to use only 14 gauge extensions in 15A outlets.Oh, I know folks do it, and I know "it works", but it is not safe, nor is it legal.
Admittedly this is less than perfect from a safety viewpoint, but the electrical code has to be practical too.