Can I add my current supervisor name in a conference paper if he pay for me the conference fees without taking a consent from my ex-supervisor?
If someone has no input whatsoever on the content of a scientific publication, they should not be listed as a coauthor. In some fields, this input may be indirect, but merely paying money never establishes coauthorship. Based on your description, it seems that B should not have been listed as a coauthor at all.
Any submission for publication needs to be done with the consent of all coauthors. Adding a coauthor is a significant step, and should not be done without the agreement of the established coauthors: So if A is established as a coauthor, you should talk to A before adding B as a coauthor.
(Edit, as Nate Eldrige pointed out in the comments): One musn't list someone as a coauthor in a publication without their knowledge and consent! If B consented to being listed as a coauthor, and indeed had no input at all on the project, this is misconduct from his/her part, too.


If B did not know about this: The straight-forward course of action would be to apologize to A and B and then to contact the conference organisers to amend the conference proceedings accordingly.

If B knew about this: In addition to apologizing to A, you should seriously reconsider whether B is a suitable PhD advisor.