I am applying for a PhD at a new university. But my grade is a little off to the scholarship line. The student service told me that I may get a scholarship, but not for sure. Now I have found two potential supervisors now. I have been working with one for years but he doesn't have much power in the university. However, another one, who he is working for and will be my main supervisor, weight a lot in the faculty. I am not familiar with the latter. Just met him once through the Skype interview. Is it polite that I ask for their help? How should I ask for the help? I am in Australia, but an international student.
It might be a bit risky and it is impossible to know what the reaction would be. However, if you actually need the scholarship in order to be able to accept any bid, then it would be appropriate for the supervisors to be told that.
If they really, really, want to accept you then it would be to your advantage that they know that you have financial constraints. However, if they are a bit ambivalent toward your acceptance, then it might be easier for them to invite someone else.
But, since you know one of them, and think he would support you, you could ask him to make your needs known to the other, rather than doing it directly yourself.
And it does no-one any good for you to hide the fact of your need.
I have only a little experience with Australian universities, but I doubt that the supervisor or your financial need is going to have much influence over whether you get a scholarship (as opposed to funding through a grant). Australian unis really want international students to pay themselves, although they do set aside a little money for international students with unusually strong research records and credentials.
To answer your question, there's nothing wrong with asking your potential supervisor, but they will probably not be able to do much to help.