What is a "voltage controlled voltage source"? How is it different from
a "voltage source" or say "current controlled voltage source"?

The terms describe exactly what they are :-)

If a voltage varies (usually linearly) in response to another voltage,
that?s a voltage controlled voltage source. Example is the signal from
a microphone going through an amplifier. The current will also be
vastly increased of course but it is usually the voltage which is
considered because the input resistance of the amplifier is usually
quite high (so doesn?t affect the voltage) and the loud speaker load
has (ideally) no effect upon the voltage.

A voltage source will give the same voltage regardless of the load,
like that amplifier. Doesn?t usually work out like this though because
the voltage source would have to be able to provide infinite current.
The definition of a *perfect* voltage source is that it has no
resistance so a car battery is a far more ideal voltage source than a
small torch battery. But up to a certain current, any decent
amplifiers will conform very closely to the ideal.

A current controlled voltage source is a much rarer beast. There are
lots of things where the voltage will change as the current changes,
such as a light bulb (though not linearly because the resistance
changes with temperature. That?s not exactly the same thing though.
But supposing you built an amplifier with a very low input resistance,
certain types of microphone will give a small current reasonably
proportional to the sound level. So if the rest of the amplifier is
conventional, you?ll get a current controlled voltage source. For
technical reasons one doesn?t usually do it this way though.

Hope this helps.

Best

Should have mentioned that the terms apply to engineering bits and
pieces, often now incorporated inside chips doing signal processing.
Voltage and current sources generally apply to component level as
well. Some are AC, as in the amplifier example, but some are DC. Just
depends on what the circuit is designed to do.

Best