At least for me, the two connectors -- 5.5 x 2.1mm and 5.5 x 2.5mm -- are very hard to distinguish with the naked eye.
I've had another quick grummage in my grotto. Out came the
BT BH3.0 with its official PSU labelled for a
BT HH3.0A, a
Huawei HG612 (3B version with the correct, white, PSU) and an
ECI B-FOCuS V-2FUb/I Rev. B with its original PSU.
In terms of plug
length, the
BT HH3.0A is the longest of them all, then the
Huawei and finally the
ECI is the shortest.
In terms of plug
diameterouter the three were compared by offering them up, end to end and considered both visually & by feel. No difference was noticed.
In terms of plug
diameterinner the three were compared visually. That of the
BT HH3.0A was clearly of a larger diameter than that of the
Huawei HG612.
So my conclusion is that the
BT HH3.0A and the
BT BH3.0 both take a PSU plug sized as 12 x 5.5 x 2.5 mm. (L x D
outer x D
inner)