Just to be sure (because I'm not):
I made dinner - I made the dinner and I finished eating that.
I've made dinner - I've made it and it's not fully consumed yet. (or maybe just because the time is not mentioned?)
He lost his wallet - And haven't found it yet.
He has lost his wallet - and probably already found it.
Simple past and present perfect always confuse me.
The usage has little to do with whether or not the dinner has already been eaten or the wallet has already been found. In fact, with the wallet example, the opposite is true of "I have lost my wallet". I would only expect to hear that before the wallet is found.
For me, the difference is simply to do with whether you are stating a fact or stating a fact which is probably combined with another piece of information, or in answer to a question.
I have lost my wallet. Statement of basic fact. (It has almost certainly not been found yet)
I lost my wallet yesterday. (We don't know if it's been found yet)
I lost my wallet in the park. (We don't know if it's been found yet)
I lost my wallet while I was in France. (We don't know if it's been found yet)
While I was travelling on the train last week, I lost my wallet.
You can say "I have lost my wallet" as a standalone sentence at the instant you realise it is missing, or any time after that, right up to the moment that you find it again.