If there is lot of dust accumulation on your rig then you'll have to clean it using compressed air but opening the PSU and cleaning it isn't a good option considering you'll have to make sure you have drained all the remaining power .I shocked myself on a capacitor once (not one from a power supply, but it was similar in size). It didn't even hurt all that much, but I wouldn't want to do it again. Instead of waiting for all that dust to accumulate and heat up your rig you should prevent all that dust build up.
I keep a small room air purifier running next to my rig. It traps all the ultra fine dust particles before it enters my PC. Also there is the added advantage of having better indoor air quality.The model I use is Clair TD 1866 ( http://go-clair.com/).This air purifier is compact and reasonably priced. It has a patented e2f filter which has hassle free maintenance and lasts for more than a year even if you operate it like 24/7.I suggest you try this option. It saved me the hassle of cleaning my PC every other month.