After electricity is generated, the voltage is stepped up at a substation, allowing electricity to be transported over long distances. Alternating current (AC) is better than direct current (DC) for transmission because it minimizes power loss. The electric company wants to lose as little power as possible in the transmission lines. The stepped-up electricity is then transported to different destinations with the help of transmission lines. Transmission lines can be either overhead or underground. Once electricity reaches its destination, another substation steps down the voltage to a level suitable for distribution lines that deliver electricity to consumers. At this point is where the designer needs a power supply. The homes are considered a secondary customer. The homes have several electronic devices such as refrigerators, computers, and TVs. The power requirements may vary depending on the device being powered in the house, and this is where a power supply is needed.