Final answer:
Primary power supplies that include class 2 or 3 plug-in transformers are used to convert higher voltages down to levels suitable for electronic devices and must be compatible with standard outlets and electrical safety codes.
Step-by-step explanation:
The question pertains to class 2 or 3 plug-in transformers which are commonly used to supply power to electronic devices that operate at voltages different from the standard 120 V AC, such as in the 3 to 12 V range. These transformers are connected to devices through receptacles and are essential for converting higher voltages down to levels suitable for everyday electronic devices. The provided figures describe the appearance and functionality of plug-in transformers and the standard three-prong plug system used in three-hole outlets. The information also includes how the plug design ensures proper connection for safety purposes and mentions how step-down transformers allow for multiple devices to run off household power supplies.
Concerning the question of the primary power supplies with these transformers, one would expect that the system should be designed to be compatible with the standard electrical outlet and to follow local regulations on electrical safety and wiring, including the correct use of color-coded insulating plastics to identify live, neutral, and ground wires.