A high-density server includes a plurality of server enclosures, each of which includes an enclosure housing with a pair of module insertion/extraction parts, a pair of power source units, a plurality of cooling fans, and two pairs of server modules. Cooling fans are linearly aligned in a crosswise direction and positioned in proximity to the rear opening of the enclosure housing with upper rear openings and lower rear openings, while server modules are installed in module insertion/extraction parts inside the enclosure housing in an insertable/removable manner. Server modules have module trays for mounting electronic components and interface units. Interface units are retractively inserted into upper rear openings or lower rear openings in connection with power source units when server modules are moved in a lengthwise direction along module insertion/extraction parts inside the enclosure housing. The server enclosure is equipped with a redundant power transmitter establishing redundant multipoint-to-multipoint connections between power source units and server modules.