The admonitions in the tier list are a general applause or warning. Nothing is 100% guaranteed. Top Dog psu right now is the Corsair AXi 1500 but guaranteed someone, somewhere got a bad one. This applies in reverse too. The avoid listing is a general warning that your chances of getting a bad psu are much greater than is reasonable. Even if it's only a 50/50 chance of a good unit, that's still not an acceptable amount. Of course this doesn't discount the fact that no matter what you've added it may not even broach 50% load, still plenty of power, but that unit might just show remarkable amounts of failure after 60% loads but is good upto then.