Wow! So much misinformation.
See my previous reply. A 15A DUPLEX receptacle is TWO 15A receptacles with a feed-thru of 20A. YES, you CAN plug in two 9A loads into a 15A duplex and it will be FINE.
Neal, I know you are a long time member here, but this statement: "I can plug in two items at 9 amps each, I have overloaded the plug and I have no protection from the breaker.", is just painfully wrong. HOW can you possibly say there would be no protection from the breaker? On top of this, the breaker protects the wire, NOT the load.
Sorry guys, but replies like this bother me quite a bit. It shows that anyone, even folks who really don't know all they should, can give electrical advice, and any unsuspecting DIYer will just read it and take it for fact.
I think he's talking about plugging into a single plug and using over 15 amps. Of course each plug can handle the 9 amps but drawing over 15 amps from a single 15 amp plug is a code violation based on 210.21B2 right? Then it doesn't matter if the internals are the same as a 20 amp receptacle or not because code states that max load on a 15 amp receptacle cannot exceed 12 amps regardless of the breaker size. And, on a 20 amp receptacle its 16 amps so we can never pull 18 amps by code.
I never meant to imply that a GFCI has any over current protection. This conversation has nothing to do with GFCI's actually.