OP is talking about the DC power feed, not a single server PSU.
But, point taken: yes your power feed should be running at <50%. But that just means you treat 50% as 100% just like any resource.
Mostly this is outsourced to the datacenter provider; they'll give you a per side rating. (usually 10A or 16A) which also matches the cooling profile of the cabinet.
However, with their comment DC == Data Center, not Direct Current.
DC = Datacenter? makes no sense, so my head replaced it with "Power Supply" instead of "DC Supply", second sentence does make sense as being datacenter though.