Hmm. You are certainly correct according to https://wiki.openstreetmap.org/wiki/Tag%3Apower%3Dportal
and
https://wiki.openstreetmap.org/wiki/Tag%3Apower%3Dpole
But I've been tagging a lot of things like this: 
https://c8.alamy.com/comp/C1Y374/uk-pole-mounted-transformer-C1Y374.jpg
and this (standalone transformer so a bit different)
https://c8.alamy.com/comp/CEPH6X/a-pole-mounted-electricity-transformer-CEPH6X.jpg
as 'portals'.
Do you think that C1Y374 image is an H-frame? The wires are not outside, but they are anchored to the top bar rather than passing inside. There are an awful lot of those terminating cables at towns and substations in the UK. I have been calling them portals for the last couple of years.

I'm pretty sure I got that from vespucci and the OSM wiki but I see what you are saying about 'h-frame'. I have certainly tagged some h-frames as portals too, as I was simply unaware of term h-frame. Clearly I need to go back and fix those.
But I'm still a little unsure about all those 2-pole transition towers, usually with a distribution transformer mounted in between them, but not always. How should they be tagged?