Final answer:
The component inside a laptop charger that converts 120 V AC from a wall outlet to a lower DC voltage needed by the laptop is a transformer. Option number C is correct.
Step-by-step explanation:
A laptop computer's charger unit indeed converts 120 V from a wall power outlet to the lower voltage required by the laptop. Inside the charger's plastic case is a diode or rectifier that changes AC to DC. Along with this, there is a transformer, which is the correct answer to the question, that converts the AC potential to the appropriate DC voltage needed for the laptop.
This process allows the adapter to charge the laptop by providing DC current. Furthermore, transformers are integral to power distribution systems to ensure the transmission of power occurs efficiently and safely over long distances.