You want to look at the physical size and specs for Bestec model#. Once you have that in hand, you compare to any similar or direct replacement PSU. So be 100% sure the model# is what is stated on the decal/sticker located on the PSU. Then do your search. If as Robert states is correct, you maybe lucky and have a common ATX-12V type sized PSU, which many are generic to your needs. BTW, having more wattage and/or connections won't hurt.
I have an HP Pavilion a6244n desktop. I need a replacement power supply for Bestec ATX-250-12Z REV D6R. Is there a compatible replacement available? Thanks!!!