There is no any impersonal Essence in Trinity, from which all Three Hypostases derive or take the power. No! In Trinity there is only one source - the Father, who eternally engenders the Son and Who eternally issues the Holy Spirit. God says that His name is "I am who I am" (Exodus 3:14), that is to say, we start thinking of God not primarily in terms of any impersonal essence, but in terms of person, hypostasis.
Now, while engendering the hypostasis of the Son, the hypostasis of the Father immediately, timelessly, without any hiatus, gives the full entirety of His essence to the Son, so that Son is fully God due to a full, essential possession of the essence of the Father, for exactly that is the meaning of the symbols "Father" and "Son": like in any natural being son possesses the fullness of the essence of the father, so it is in relationship of the Father and the Son, but in difference from natural created beings, in which the son's nature comes from potentiality to actuality in a process, in relationship of the Father and the Son is not any process, but Son is immediately, eternally perfect just as the Father is (Hebrews 7:28). And, similarly, when Holy Spirit eternally, without any hiatus, proceeds from the Father, the Father gives to the Holy Spirit the whole entirety of His essence, just like in the instance of the Son, and so the Holy Spirit is fully God due to a full, essential possession of the essence of the Father, thus, like Temple is a Temple of the Perfect God, so that if it is a Temple of anything less than Perfect God it is no more a Temple in Judaic Monotheistic context, so when Paul calls us "Temples of Holy Spirit" (1 Cor. 6:19), he cannot do so without considering the co-perfection and co-equality of the Holy Spirit with the Father, which can be possible only if the Holy Spirit possesses from the Father the entire fullness of His nature/essence.
This being established, one can safely proceed. Now, what is power? Can it be considered separately from essence or it is a part/aspect of the essence? Of course the latter is correct: the power is an aspect of the essence, as is will, as is wisdom, as is goodness etc. Thus, to say that Son possesses the full entirety of the Father's essence but lacks full entirety of the Father's power is as absurd as to say: a candle that is lit from another similar candle burns with the very same flame as the first candle, but still this flame is less efficient than the flame of the first candle, like in a Chuck Norris joke: "If you have only five dollars and Chuck Norris has only five dollars, Chuck Norris has more", yet we are not amusing ourselves now, but doing theology, which is a serious matter and not so much amusing as amazing.
That Father gives birth to the Son and issues the Spirit, this necessary theological/ontological fact does in no manner make Father the "only almighty", for the fatherness of the Father depends on Him engendering the Son. Begone with the Arian blasphemy that God was initially sterile, non-Father, and then, having created Logos, he became also Father, which was not His eternal and necessary name! Rather, "father" is God's eternal and necessary name implying that He eternally has also the Son. In this manner, the Hypostasis of Father, in order to justly possess this eternal name, depends no less on the Hypostasis of the Son eternally born from Him, than the Hypostasis of the Son depends on the Hypostasis of the Father giving birth do Him, for only through the birthgiving any father is and can be called father.
Moreover, power is there for activity, for God does not possess any passive power but active power. Now, can Father ontologically act without the Son and Spirit co-acting? No, He cannot! Just like the disc of the sun cannot enlighten and warm-en (I like to say "warmen" as a verb rather than "warm", even if not according to normal English) anything without radiation of its rays and warmth. Thus, when Father acts, He does so only through the Son and Spirit co-acting, and the same is true with all the three Hypostases' divine activities (cf. St John Damascene: “The Father is a sun with the Son as rays and the Holy Ghost as heat” /The Fount of Knowledge; The Philosophical Chapters, on Heresies, the Orthodox Faith (The Fathers of the Church, Vol. 37) p. 162/).
In fact, only the Incarnate Son can also act humanly, for Father and the Holy Spirit cannot eat honeyed fish, appreciating its taste, as the Lord did (Luke 24:42), and neither Father, nor Spirit can enjoy the taste of wine (Matthew 11:19). Does this make Son more powerful than the Father and the Spirit? In a certain sense, yes, but I would not call it "more powerful" but "broader" for Son's activities include both divine and human activities, whereas the Father's and the Holy Spirit's activity is only divine activity.