To upgrade a separate power supply?

Or, how many years since it was last turned on? If it's in frequent use and working correctly, it may not need replacement electrolytic capacitors. 

After how many years should the caps be replaced.?

Look here

and here.

@hilde45 . Thanks. Very helpful.

Thanks to @hilde45  hilde45 I know to just replace them. Thanks also to Paul McGowan of PS Audio for informative clips.