What's the model number?
If you have the regular power + 4 pin aux power, and SATA power leads, you should be set. Power supply standards have changed very little over the years. You may have issues with video card power, but adapters can take care of that.
Model No: ATX-550w
AC Input: 115/230v~,10a/6a,50-60Hz
DC output: 550w
+3.3v +5v +12v1 +12v2 -12v +5vsb