Sadly, neither, as I've been hunting for a Dell Optiplex chassis to mod and the sad fact is that the USFF and SFF versions are on a proprietary unit altogether. While the bundled PSU that comes within these compact systems are rated to be at 80 plus gold efficiency their replacements aren't as forgiving and seem more like paper weight. You should know however that the DT version's unit is TFX supposedly from the
dimensions.