Behind this question is a quiet fear: what if the One in charge isn't safe? Scripture takes that fear seriously. The Psalms shout it. Job lives it.
The Christian answer is not a philosophical proof of niceness — it's a face. "He is the image of the invisible God" (Col. 1:15). When we want to know what God is like, we look at Jesus washing feet, weeping at a tomb, refusing to call down legions of angels, and bleeding for those who mocked him. God's omnipotence is defined by Calvary, not the other way around.
The Orthodox lens
The Fathers insist God's "attributes" are not pieces of him. St. Gregory Palamas teaches that goodness, love, and power are not separable in God — to encounter his power is to encounter his love. That is why the Paschal liturgy can sing of a King who reigns from the tree.
The modern voices
Tim Keller put it well: a god of pure power would be terrifying; a god of pure love would be useless against evil; only a God who is both can be trusted with our suffering. C.S. Lewis added that Aslan is not safe, but he is good — and the difference is everything.
If God's goodness still feels distant, start where the disciples did: at the foot of the cross. The proof is a Person.