I would recommend you to get a power supply that meets the requirements for your card though. 650w might be sufficient for some people or brands but there is no 100% guarantee that the same rule applies to you. I wouldn't take the risk and just get a new power supply that meets the requirements. In the end it is up to you if you want to take any risk or not.
Edit: 650W does seem okay imo but I just would meet the requirements to be sure.