A larger power supply is only likely to outlast a smaller one, assuming they are both used within their load rating, if there is a quality difference between the two.
In other words, in order to get a cheap power supply to last longer, you generally have to oversize it.
I don't know about scientific studies, but reading jonnyguru.com is very educational.
Besides component quality, things like OCP (Overcurrent Circuit Protection) is very important for both power supply and system life if a rare short circuit occurs. (Or not-so-rare, in the case of USB ports). My most recent system loss was an old, cheap but pretty group-regulated supply that was supposed to have OCP, but didn't, and died when a USB port shorted. It died, completely, along with the USB functionality of the M/B.
Power factor and conversion efficiency should be considered. Generally speaking, power supplies lacking the 110/220 red tab on the back are higher quality. Supplies with an 80+ certification, better still.
It is a complex subject, but generally speaking, if you pay more for a quality power supply that is 80+ bronze or better, you are getting a better, longer lasting, more efficient P/S.
If you pay less for a larger wattage p/s, the extra wattage increases the possible damage it can do.