Registered as "http-mgmt" with no public specification — in practice just another HTTP admin port.
IANA lists 280 as http-mgmt, assigned to Adrian Pell, but no protocol document was ever published for it and no widely deployed product claims the name. What actually turns up on 280 is ordinary HTTP: a device or appliance whose web management interface was moved off 80, or a proxy or admin console picking a low free port. Treat it as unidentified HTTP and confirm with a request rather than assuming the registration describes the listener.
Expose with care
If this is a device management UI it is cleartext HTTP with a login form — fine on a management VLAN, never on a public address.
$ curl -sSI --max-time 5 http://TARGET:280/Seen this on your network? Beige Box scans your Wi-Fi and shows every open port on every device — and its Ports tool links straight back here.
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Corrections or a missing port? Reply @rimrocksystems.