According to Edwin Pawlowski :

From the description, you have a GFCI receptacle.

Actually, a GFCI _plug_ on the A/C cord.

It is needed for certain
uses, normally outdoor, kitchen, bathrooms where electric appliances are
used near water. They sometimes trip out with appliances, even if there is
not a ground fault.

There does not seem to be much evidence of that happening with appliances
unless they really do have a fault.

To answer your first question, if it is that type of receptacle, yes, it is
grounded.

Uh, not really. GFCI outlets are a legal substitute for grounding
with old circuits that have no ground. The GFCI doesn't create one -
it provides alternate protection.

If the house was constructed prior to about the mid-late 60s,
it probably doesn't have a ground (or at least, not a very good one).

Since this isn't a GFCI receptacle, the only "downstream" is the A/C
itself.
--
Chris Lewis, Una confibula non set est
It's not just anyone who gets a Starship Cruiser class named after them.