The easiest way to say “Yah’s power” in Hebrew is to follow the names which use that very phrase: עזיה ˁUzzi-Ya (Amos 1:1), or more fully עזיהו ˁUzzi-Yahu (Isa 6:1). However, one can find that very phrase used in Numbers 14:17 כח אדני koaḥ ʼAdonay (כח יהוה koaḥ YHWH in some MSS).