Ever see a boxing match where the slower fighter's reaction time allows him to eat canvas to the count of 10?
A joule is yet another buzzword. By itself it is as useless a term as "best" "surge protector" and all the rest of misused terms. Ninety nine percent of cheap strip protectors use a clump of dirt cheap MOV's metal oxide varistors and go on to chortle how many "Joules" of protection their gizmo offers.
To protect against sluggish voltage variations voltage correction is necessary
To protect against slow-motion "surges" MOV's are appropriate
To protect against damaging high frequency transients, gas tube discharge and avalanche device protection is mandatory.
It pays to know what's inside your "miracle" gizmo.
I believe I have several tens of millions of joules worth of 330volt MOV's stuffed in a drawer somewhere. I used to buy them by the pound.