It's hard to explain without pictures, but they are different shapes. If you go here:

http://www.hubbell-wiring.com/new/hub9811.pdf

You can see on page 2 a 15 amp receptacle on the left, a 20 amp on the right. The 20 amp is designed to accept either a 15 or 20 amp plug.

I could be wrong, but I suspect a device with a 15 amp plug shouldn't draw more than 15 amps over the long haul, discounting surges and so forth.


Charlie