the actual device i mention in the video 2N6027
it is still available from mouser, and is a few $ if you like to play with it.
is a low power signal level kind of part, used to trigger bigger parts that handle the power you need,
and its gate polarity is the other way arround, compared to SCR and TRIAC,
that is why i found it interesting to play with PUT and to explain it, since no where i looked online,
no videos, revealed the important gate polarity and what terminal is its refferance,
the parts you mention for light dimmers, are TRIAC
they are like an SCR, but double, so they can be used for AC