Which of the following theorems is applicable to both linear and nonlinear circuits?

While calculating Thevenin resistance (Rth) or Norton resistance (RN), independent constant current sources in the circuit are:

While calculating Thevenin resistance (Rth), constant current sources in the circuit are:

According to the Maximum Power Transfer Theorem, maximum power is delivered from a source to a load when the load resistance (RL) is equal to the internal resistance (r) of the source. At this specific condition, what is the efficiency of the power transfer?