"my power" is metonymy for the ability of the king himself. AT: "from me" or "from the power of my army" (See: [[rc://en/ta/man/translate/figs-metonymy]])
This can be expressed in an active form. AT: "Yahweh will never allow the king of Assyria's army to take this city" (See: [[rc://en/ta/man/translate/figs-activepassive]])