There is a way to tell the source of the electricity, but to do it you will need a microscope with very high magnification, ie an electron microscope.
If you examine the electrons coming from the wall socket, you will see that there are several distinguishing features:
Dark brown electrons = oil fired power station
Black electons = coal fired power station
Electrons which shine brightly = Solar power
Electrons surrounded by fast moving clouds = Wind power
Electrons which have a film of water = Hydro power (or subsea turbine, rare, still very experimental)
JimB
(In frivolous mood, the sun is shining, the weather witch says it may last for two days or so)