i've just left a position at an IT field support company, where one client had around 15 of the optiplex sx280 machines (bought in around 2005) with this faulty capacity problem. up to now, they've been lucky and had only 6 of them fail.
in response to christian, i looked at attempting to replace the blown capacitors with better japanese caps. it's not possible due to the 4 layer motherboard. where that you could attempt to get clever and snip the old capacity away and solder a new one to the "stumps" that are left behind, removing the capacity is not feasible due to not knowing whether or not it's soldered into the middle layers, and not actually being able to get to it if it is.
either way, it's not really feasible to attempt to repair these machines. it was also doubtful as to whether if we were to replace the faulty capacitors if the machine would even still work, since the affected caps regulate the power to the cpu and surrounding circuits.
in the current day, the affected machines are so out of date, it's probably worth updating anyway!
what's more scary, is i've seen the SAME capacitors, and the SAME failure in SERVERS! i've seen server motherboards fail (poweredge 700/800 series), and dell pci-e SAS cards fail, with the same blowing/boiling capacitors as seen in the sx270/280 and gx270/280 series desktop computers.
so many levels of fail by dell. shortly after we discovered this problem, we stopped selling dell machines entirely, and shifted to hp/compaq.