Asking for funds to attend a conference from a current advisor for previous work
Professionally, you should first explore the possibility of funding from sources other than your current advisor, e.g. the conference organisers or third-party sources. Ideally, your previous supervisor should help you out in this process. If your paper has good reviews, then you can feel more confident with your efforts. Does your previous supervisor know people in the conference organising committee or the professional committee under whose umbrella the conference is being organised (e.g. ACM or IEEE sub-committees)? I don't imply anything unethical, but your professor could use this informal channel to better gauge the waters, which might help drafting the funding appeal more effectively.

If the above course of action is not feasible, try to ask your current supervisor  for ideas, without directly asking for funds. S/he might be able to suggest other sources, and help you with the application process. You might eventually be able to appeal to the benevolence of your current supervisor, but you must first demonstrate your diligence in pursuing other avenues. Remember, faculty members are always pressed for funds. If your current supervisor is unable to help you out, it wouldn't necessarily mean that s/he is unwilling.

If all everything fails, you will have to communicate with the program chair and indicate your inability to attend. Assuming that you can arrange funds to at least register (this should be your minimum ask from any funding source), it might be possible to arrange for another speaker to make the presentation on your behalf. Explore the possibility of presenting via Skype. Try to find out from the conference chair whether any of this would work, and work with this as your fallback.

Remember to use the good reviews to your advantage while making your case. All the best.