Seems that the private key that I have, is a bitcoin one, but it also fits with the Stellar (and seems that are funds in it).
So, not sure if any distinct private key format would be the best choice to assign it to a specific crypto. From here my question if exist a way to do it automatically (generate the public key and search it in the explorer)
I don't think it's a good idea to keep importing it to different wallets in an online PC if you indeed found one like you said you found a balance on Stellar I suggest transfer this funds right away to a new wallet.
I guess you already found the right one. Stellar should be the coin you are looking for if you found funds on that wallet. If were you transfer it right away.