God is the foundation of existence.
He's All Powerful in relation to his creation, because everything existing (space, time, matter) depends on him to exist, so everything is naturally less powerful.
So you can't ask if GOD can create something more powerful:
It's like asking can water make itself wet?
Can fire burn itself?
Can light illuminate itself?
The reason we have the concept of power is because we relate ourself to him. If he didn't exist, nothing would exist, hence the concept of power wouldn't exist.
You gerrit?
So can GOD create something more powerful? The answer is you're asking the wrong question.