All my current computers use Antec (Seasonic built) power supplies and as and when I've needed another, I have put the new one in my main rig and moved the others down one so that the older power supplies are used in the least frequently used computers where they are under less load/stress. Once they are out of warranty, I open them up every few years to give them a good vacuum out and a general visual inspection. The only issue I ever had was when one of the modular SATA outputs stopped delivering 12 volts but that was traced to a dry joint that was repaired with a blob of solder. Some of them are well over ten years old by now and still seem to be ok.
One surprising PSU I came across was a cheap unbranded one I bought new about 12 years ago from a local shop for £20. It was meant as a stopgap for a friend who ran a garage and needed to get his PC working urgently as he relied on it for all his invoices and it was costing him revenue. The PSU was only meant to last a few days whilst I ordered him a decent one online. However, because the PC was now working and he was always producing invoices, he kept postponing the date to change the PSU and it ended up never getting replaced. Two years ago he sold the business and gave me the old computer for parts. The PC had spent its life under the desk on the floor and had operated for twelve hours a day, six days a week for over ten years. The PSU was full of fluff and other workshop detritus, but it had never faltered once in all that time. One thing that may have helped was the workshop was unheated, cold and draughty all year round and the PC had a good supply of cool air. Also, it was only running Windows XP with a Microsoft Access based accounting programme and was never under any real stress. Should it have been used in a way that demanded more from it, it may have had a much reduced lifespan.
