While the Prime maintains its position as the best PSU line available anywhere at any price, (tho I am by no means complaining as the cost is very reasonable) the 12 year warranty has no real significance to the consumer except in their mind's eye.
Take any PSU and add a price premium to cover the amount of money that needs to be set aside to pay potential future liabilities and you could extend the warranty by as many years as you think will make consumers buy your stuff.
I have several X series units here all humming along, tho i have to say humming is bot quite appropriate wording since they all run dead silent. That and the Antec CP-850 units have been among the quietest we have ever owned.
Only really annoying PSU we've had sound wise has been the EVGA G2 1000. Have used several B2 750s w/o issue and used G2s in several sizes in user builds ... you can hear them if you pay attention but otherwise not. My son went looking for a G2 850 about 2 years back but chose the G2 1000 as it was on sale and w/ MIR it was cheaper than the 850. With twin 970s in SLI and 9 fans in the case, the PSU fan was the only only sound emanating from the case.
Wrote it off to the luck of the draw as others had not reported this but when it failed about 4 months ago, EVGA quickly replaced it, but the 2nd unit is as noisy as the 1st one.