this is the most powerful (ahem) ....upgrade i was able to find for the slimline
http://www.atxpowersupplies.com/270-watt-HP-slimline-power-supply-FSP270-60LE-SL.php

Yeah , none of the "little PSU" that I found pass the 270w mark.

Check this. http://http://www.directron.com/fsp27060le.html

and this http://www.censuspc.com/Sparkle-Power-SPI270LE-270-Watts-FLEX-ATX-20-24-Pin-RoHS-Power-Supply-Bulk-pack-pr-5902.html

Now I found this 300w woot! http://www.directron.com/flex0130b.html

***UPDATE***

Im now thinking on moving the insides to a bigger case, so I can just get a decent PSU plus I get the extra space and ventilation.

This might be my choice : http://www.tigerdirect.com/applications/SearchTools/item-details.asp?EdpNo=5250569&CatId=32
This should work right? I mean, as far I could research, my motherboard (HERE) should fit in there without any problems right?

Anyway, any suggestions?

red1776:
the site you mentioned is about to release a device that can power the video card from outside the computer case without disturbing the existing power supply configuration.

disclaimer: I am affiliated with the site that red1776 mentioned.

Are you aware of any higher wattage Power Supplies than the one red1776 mentioned (270 Watt )

Sure!

After some hours (literally) of searching I found this one. Seems reliable and well , the best mini-PSU of 270w+ available out there.

300w mini-PSU : http://www.directron.com/flex0130b.html

Could you link it please?

Care to explain?