"If I would have" vs "If I had"

What is the difference between :
- If I had done this I would have been successful
and
- If I would have done this I would have been successful

I'm not a native speaker but although the second sentence is used a lot it sounds very incorrect.

The second one is not correct.

The conditional perfect can only go in the "then" clause - it is grammatically incorrect to use the conditional perfect in the "if" clause.

People use that second form a lot, although I wouldn't call it strictly standard. A lot of people, myself included, probably wouldn't use it very often.

I have never heard anyone say 'If I had done'
I think what people actually say is "if i'd have"
which sounds like "if'i'd've" when said fast