Sal,
I believe you nailed it - I too believe most converters are not run near their max for more than a very short duration. Most converters run two large caps on the input stage in parallel after the full wave bridge rectifier. Guess it's lower cost to get two smaller ones than one large one and might be easier to get in the space requirements.
From what I have seen much of the time it's a heat related issue that destroys the components. The high failure items are mechanical as in the fan stops after getting full of dust and dirt and it's only a matter of time before the unit dies from excessive heat.
Sure hate to see folks toss good converters / inverters / electronic devices in the trash when normally in less than 30 minutes they can be as good as new for very low cost.
