Power distribution in data centers used to emulate the architecture of old telephone central offices. A “rectifier” would step down and rectify the ac from the power line and use it to charge banks of batteries that provided an unregulated 48 V dc, which was distributed around the facility to run the telephone equipment in the racks.
Since at least 2007, data-center engineers have been talking about distributing 400 V dc (sometimes 380 V). Data centers are bigger and use a lot more power than telco central offices. At a minimum, higher voltage distribution would mean lower I2R losses and/or thinner power-distribution cables.