you can also use an older AT supply.
but you need to load the 5V side of the PSU, or you wont get much current from the 12V rail.
i used one modified to power my older 12V powered chargers.
i had to put about a 5A load through the 5V side of the PSU, or i was unable to draw more than
about 3A before the PSU would shut down. i used a pair of ceramic resistors calculated to give about 5A load on the 5v side.
both were sandwiched between large heatsinks to keep them cool. this worked great, and it's still working some 15 years later.
i have given this PSU to a friend, as i now have a Hyperion and a meanwell 24V 1000W PSU.
Jason.