Without stating what the make and model of your PSU is, and also stating you're not sure if you can work with an adapter is the exact reason we ask you to state the make and model of the PSU and it's age.
FYI, thumb rule, if the PSU lacks the necessary connectors for your components, the PSU isn't meant to be paired with your system.
To add, with that GPU in your system, the entire system will need a minimum of 600W of power from a reliably built PSU.