Above figure shows the transformation of a circuit to its Thevenin equivalent. Imagine this is a power supply and A is the + terminal.
In reality the real circuit model is the one on the left side and just before the A terminal I circled the resistance with red color.
On the right side is its Thevenin equivalent and the Thevenin resistance is circled with green color.
I have the following questions:
1-) When one talks about the "output impedance" of this power supply, would you understand the red or green circled resistor?
2-) Lets say you don't know what lies inside the black box. You can measure the Thevenin voltage across A and B terminals by a voltmeter. But is it also possible to quantify the Thevenin resistance Rth(for example by shorting A and B)?