Garbage disposal

Plas, a typical US receptacle is rated at around 15 amps. Somewhere on the disposal you should find the power consumption. Watts is volts times amps

https://www.google.ca/#q=current+rating+of+typical+US+power+receptacle

One might guess you simply wore out if not overloaded the top receptacle

I assume you don't have a split wired receptacle under the sink and the disposal is controlled by a switch at the counter. If the entire receptacle is controlled by the switch and 1/2 is not working, then replace the receptacle. If you want to know if the receptacle is damaged then turn off the breaker and remove the receptacle and look at it. You can get a new receptacle at any hardware store. Since your disposal is working, I would think it's fine.