I have recently cleaned a Quicksilver machine. The iFixit guide should be helpful to you.
But in my opinion, there is something even more critical when it comes to cleaning than the power supply: The "big fan". This one is sitting below the PS and can be opened relatively easily. Behind it, there usually is quite a bit more dirt than in the PS...
To clean the PS, you don't actually have to remove its wiring completely. If you turn your Mac in a "reversed L position" (on a couch, for example), so that the tower is lying there in front of you and the side panel is mounted against the couch backrest, you can get it out whilst keeping the wiring as it is.
If you really intend to open up the PS (only 4 screws on the QS model), I would suggest you swap the fan inside it. It's a standard 80x25 mm fan, you only have to flip the power cables.
Good luck :-)