"Good job" is a common expression. I've never heard of "more power to your elbow." (I am a native English speaker.)

“More power to your elbow”? I’ve never heard that before as an American English speaker. American English does have “more power to you”, but not as a straightforward expression of approval. The context is more like “If that’s what you want, [not that I’d choose that myself], then more power to you.” Americans do say “good job”, but often to kids. Other very general expressions, especially when someone does something difficult in sports for example, would be things like, “that was great”, “that was awesome”, “you did amazing”, etc. Is this the context you mean?

As an American, I would simply say "good job" or "great job" or "you did an awesome job". I've never heard of "more power to your elbow" so I would be confused if you said that one.