For any communication network, DC power supply is the backbone of system. Reliable DC power supply system increases communication system reliability. Normally the power systems consist of Battery Chargers / rectifiers and Batteries, the Rectifier converts the incoming AC in to required DC voltage, this DC voltage is used to power the load equipment and at the same time is used to keep batteries fully charged. The battery is required to provided backup power in case of mains failure. Depending on the system, application and required availability, power system is sized and configured. Where high reliability is required normally parallel rectifiers are used to provided redundancy. Modern SPMS rectifiers are based PWM technology and are very compact compared to traditional rectifiers. There are no transformers used to stepdown the voltage hence efficiencies are higher (>90%). The physical sizes of power systems are also smaller for similar capacities compared to traditional rectifiers. Most manufactures are using this technology to produce power rectifier modules of fixed power rating and these modules can be paralleled to increase the capacity.