As long as it's not a DEL, they tend to be one of the few manufacturers (the only one?) that use none ATX standard parts... then you can pretty much buy what ever one you want.
As to the power output. Assuming you have not and are not thinking about upgrading other components (and hence requiring more power) then you could buy the same wattage. Though for the difference money wise, you might as well go for something like a decent 350w.
and yes... all ATX standard PSU's should be pretty much identical in size etc. even down to where the screw holes for fixing them to the case are.
Have a look at a WEB site like click here they have a decent range.