Not necessarily. I have a HP Z400 workstation with what appears to be an ATX PSU... but some of the pins are swapped and it won't actually boot with a non-OEM PSU. You can make an adapter, but in general it's not a safe assumption that this class of systems are compatible with off-the-shelf PSUs. These are OEM systems and the only thing that is guaranteed to work is OEM parts.

https://www.badcaps.net/forum/showthread.php?t=47754