The diagram below labels the main components of the charger. AC power enters the charger and is converted to DC. The PFC circuit (Power Factor Correction) improves efficiency by ensuring the load on the AC line is steady. The primary chops up the high-voltage DC from the PFC circuit and feeds it into the transformer. Finally, the secondary receives low-voltage power from the transformer and outputs smooth DC to the laptop. The next few sections discuss these circuits in more detail, so follow along with the diagram below.