[baybal2]

The telecom industry has 48 volt as a de-facto standard, bur never came to a mechanical standard.

Thus you see daisy chains of mechanical adaptors in telecom closets.

[kjs3]

Well...the daisy chains were the standard for mechanical connections. :-)

What there never was was a connection standard safe enough to put in a house, made to be (ab)used by normal people. 48v DC as it lives in the telco world is flat out dangerous if you aren't careful.