The document compares and contrasts AT and ATX power supplies. AT power supplies were commonly used with older PC systems and provided power directly from the AC outlet. ATX power supplies became popular with newer systems and include additional safety features like a fuse and switching circuitry. The ATX design steps down the high AC voltage, rectifies it to DC, filters it, and regulates it to stable voltages needed by PC components. Higher wattage ATX power supplies are needed to support more powerful modern components like high-end CPUs and graphics cards.