Greetings,
Welcome to the forum.
I am not a HP employee.
The latest HP systems are using proprietary MB connections.
You will have to get a HP PSU if your system qualifies.
But you need to provide the full product or model number.
The HP Parts Store or HP Part Surfer would be the place to go. The problems is we need to find the 500 watt HP PSU part number or a different 690 PC with a 500 watt PSU.
I had some PSU part numbers for the new systems but have lost them. Maybe someone else has a 500 watt PSU part number or PC part number having a 500 watt PSU that will work in your new HP.
I have been looking for 690 systems at the HP Store. It seems the 690 uses a 310 watt or a 400 watt PSU.
You may be out of luck on finding a compatible 500 watt PSU for the HP 690 series.
Regards