It may not be fully consistent from machine to machine. It is at least in part a question of space for the text in the GUI: some machines have very short status text "OFF" / "Idle" / "Running" and the phrase "Not Enough Power" is too long for the same space, so "No Power" is used as a shorter alternative.
It may also be history - Galacticraft grows organically, code for different machines may have been written 4 years apart. A developer coding a new machine (me or Micdoodle8 most likely...) will tend to base it on the most similar existing machine.
There was an attempt to harmonise several of the machines when you raised the issue about the "OFF" status display for machines which are redstone disabled, so most redstone disableable machines should have consistent displays but even there I think they have the choice of short or long text for "Not Enough Power".
I'm not totally sure how this is handled in other language versions, but if the translators are smart they will check how the GUI looks and will aim to match - roughly - the size of the English strings.
