Precision 3660 Power Supply

I have a Dell Precision 3660 with a 300W PSU, I want to install a GTX1660 GFX into it but it requires a minimum 450W PSU. I know that there are 500/750/1000 W options for that range of workstations but no one seems to sell them. Has anyone had this issue and managed to purchase a 3rd party PSU that fits. It's a half size PSU. Thanks