I am posses a high level of expertise at this stuff.
Basically, in general sense almighty, all-powerful and omnipotent are synonyms, which means you can use them interchangeably talking with other people. However, one really important aspect of language that AI didn't conquer is context. In different situations, these words may change their meaning and be no more synonyms of each other. For example, the word “composing.” It may refer to the process of creating/narrating, practice or hobby of creativity, art of creation/narration, etc. Impactful forms in English open great possibilities for context to appear.
The same way within this community, we define Omnipotence as the one state of being able to do anything, which pretty much is all-powerfulness and almightiness. So, yeah, they are synonyms but they may change depending on what kind of Omnipotence you mean. We use more complicated and theological concept to justify its difference with Metapotence, so in some cases you may refer to Omnipotence as the power and competence to do absolutely anything (which is more accurate to say it's Metapotence) or as incomprehensible state of being above all, which includes such properties as Omniscience, Absolute Transcendence, Eternal Existence, Indeterminacy and infinitely more. Neither way Omnipotence can be interchanged as "almightiness" or "all-powerfulness" but you should see distinction between those two take-ons on this concept.