Standard ATX power supplies can work with that model. The only thing is the fitting into the case. The location of the power switch and power connector on the Antec, does not match with Dell's case. Even if you turned it over. Unless you feel like cutting an extra hole.
They do sell specific replacement PSUs from PC Power & Cooling, but those have been discontinued.
I found another PSU that looks like it can fit (power switch and connector are located in a similar spot compared to Dell's PSU), but I cannot guarantee that. You might have to do a little cutting.
Newegg.com - FSP Group SAGA+ 450R 450W ATX12V Power Supply - Power Supplies
I've done this before on one of my friend's Dell. He too had a Dimension, and needed a PSU replacement. So I ordered the 400W version of the link I provided earlier, and found out that we had to bend the hole a little larger on the back of the Dimension case to accommodate the power switch of the new PSU.