Jehoshaphat uses this rhetorical question to emphasize that God is in heaven and his authority over all things. This question can be written as statement. Alternate translation: "you are indeed God in heaven and the ruler over all the kings of the earth." (See: [[rc://en/ta/man/jit/figs-rquestion]])
The words "Power" and "might" mean basically the same thing and emphasize the greatness of Yahweh's power. The word "hand" refers to possession. Alternate translation: "You possess great power" or "You have great power and might" (See: [[rc://en/ta/man/jit/figs-doublet]] and [[rc://en/ta/man/jit/figs-synecdoche]])