Caps tend to leak with use(and heat generated from use).
The problem with long times without use could be caps drying(electrolytic caps do this.) out. I think it would take more than 5 years.
On the same note, I pulled some caps from a drill charger WAY older than 5 years not used for much longer and they still work
. Bad caps are much more of an issue when used for long times at hot temperatures.
What power supply is it anyway?