You should replace a PSU about every four or five years yes.
They become less efficient through use, and less stable when it comes to producing power. due to the age of components inside and heat produced.
They start off glitching and then slowly get worse and more frequent.
Shut down of the system, BSODS, and resetting of your computer when heavy power load is required from them.
Overclocking of components can cause the same problem.
And backing any overclock off components in the system if you have overclocked components may stabilize the system under heavy power usage..