Unless you are willing to cut your case, any PSU with a 120mm fan in the top will be a problem as they need pretty much a fully open back panel for exhaust. What I mean is the area DIRECTLY BEHIND THE PSU needs to be open, not anywhere else on the back of the case. Right now you only have an 80mm fan opening. You can get a nibbling tool at Radio Shlock or from jab-tech.com to cut out the back of your case as needed - not too expensive and it will strengthen your fingers and wrists (trade off hands for balance) .
Note how the back of most generic cases look these days. There is just enough metal there to hold the PSU mounting screws and all the rest is open. That allows you to use any type of PSU - one like you have now or one with a 120mm fan or other arrangement. If you're gonna cut, I suggest that's how you cut. Go to a friend's house who has a generic ATX PC. and trace the back of his PSU opening along with locations of the four PSU mounting screw positions and you'll have a template for your cutting.
All you need to do is find a PSU with an 80mm fan in the rear w/o a switch and you shouldn't need to do any cutting. I thought you had one located at ZZF or some such - didn't that FSP-350-60PLN work out? It looks like the 300W unit next to it has the same picture - or did you already check that ) or is it too weak) The buildtoorderservers link I gave you in the other thread does appear to have a lot of switchless PSUs like yours - check them out.
Another option (as was mentioned in the other thread) is to get a PSU that would otherwise work but for the switch (like the Sparkle at ZZF) and remove the switch. That is easy to do and is easily reversible when/if needed. Just cut the wires off the back of the switch and connect them together with a wire nut. Then push the switch out from the inside out. There are a couple of ears on the switch inside the psu case, just squeeze those against the sides of the switch and it should slide right out.
I have 25+ years experience with PCs, so generally you can rely on what I tell you. If I'm not 100% positive as to my advice, I usually qualify it.
.bh.