When trying to perform any authentication-related operation in Git for Windows you may hit the wall with:
Couldn't agree a key algorithm (available: list of available methods)
Some people says (here and here for example, but also in many other places) that this is due to your PuTTY not being up-to-date and ordering getting latest version of PuTTY as a cure. You're lucky, if that works for you! :>
I wasn't that lucky and it turned out that in case of my Git for Windows TortisePlink was actually the problem.