Source transformation

The transformed sources are considered identical and can be substituted for one another in a circuit.

[2] Source transformations are not limited to resistive circuits.

However, this means that source transformation is bound by the same conditions as Thevenin's theorem and Norton's theorem; namely that the load behaves linearly, and does not contain dependent voltage or current sources.

has value equal to the ideal current source's value times the impedance, according to Ohm's Law

Source transformations are easy to compute using Ohm's law.

In the present context, it implies that a black box with two terminals must have a unique well-defined relation between its voltage and current.