Switch Mode Power Supply (SMPS) applications generally involve power adaptors, desktop power, or server power. SMPS design is separated into primary and secondary sections due to isolation topology. The primary section involves EMI filtering, input rectification, and power factor correction (PFC) devices. The most important design concept is PFC to improve efficiency. Good performance of a PFC rectifier enables the power supply to operate efficiently under a light current load. Ultra-fast recovery time of the rectifier and low Qg of the switching MOSFET are the most important factors associated with PFC. No matter what kind of topology is involved, PFC is the key not only to increasing efficiency, but also to improving thermal performance, especially for 80-plus SMPS. For EMI, film capacitors and ceramic disc capacitors are good for X-capacitor and Y-capacitor design, respectively. Regarding input rectifier devices, single-phase bridge rectifiers are the best solution, especially for power adaptors. The secondary section includes output rectifiers and filters. Trench MOS Schottky technology is a new technology that can replace planar technology as a non-synchronous rectifier solution. Its key feature is ultra-low forward voltage, or Vf. Trench MOS Schottky rectifiers work well as output rectifiers, especially in multi-output systems. In addition to providing good forward voltage performance at high ambient temperature, they also feature high current handling and voltage (up to 150 V) capabilities. Different solutions are based on different specifications.