Back 'in the day', I remember Sun selling servers being available with 48VDC power supplies especially for the telcom industry.
Most CO's (central office exchanges) had to provide at least 8 hours of service even with power grid not available, so to do this they really ran off of large banks of batteries... 48V DC was the preferred. And it was used for all the switching and related equipment at the CO. They charged the battery bank from commercial power, and normally have generators for when the commercial power fails, but still everything ran off of 48VDC. If you needed AC, you had to run an inverter, but again, it had to take in 48VDC. Why 48VDC? I am sure it is in the history books for the Bell System and Western Electric somewhere. If someone knows the original reason, I would be interested. In any case, legacy 48VDC system are there, and some vendors take advantage of it, since telcom is a pretty big market and the infrastructure for distributing the power is already well developed. If they need some other voltages, they invert it and use appropriate switching power supplies to get the desired voltage.
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