Chapter 2 of the 1689 confession on God and the Holy Trinity says, self. Is alone, in and unto Himself, all sufficient, not standing in need of any creature which He hath made, nor deriving any glory from them, but only manifesting His own glory in, by, unto, and upon them." So when we talk about the self-sufficiency of God, we are saying that God is sufficient in and of himself. God needs nothing else. God needs no cause for himself. He is his own cause.
And he says in the Psalms, if I were hungry, what I tell you? No, I own the cattle on a thousand hills. Because our God is self-sufficient. He's all sufficient unto himself.