Normaly caps can pop when the dissipate to much, they get hot, expand and pop open. The dissipation can be caused bij to much DC leakage or dielectric loss, ESR etc. If they are not used for a long time, like 10 years, the caps lose most of their oxide layer. And without that you have a problem if you not reform the cap before use.
As far as I know it can not pop new in the box. It will only pop if you use the psu.
So, if you found the popped cap before you powered it, it was not new. If it bpopped after some use, it is your own fault, never power up old stuff like this whitout reforming the caps. If they used very good parts and a good design there is a change you have luck but if it is china crap it will fail soon.