Taken from an article on "9 things you should know about surge protectors"
Power strips and surge protectors (also called surge suppressors) are different;
Power strips are cheap, multi-outlet products that are merely an expansion of a wall outlet. These usually have a circuit breaker of some sort, but most don't offer any real "protection" from electrical issues. Some might have the barest level of protection, but they're all pretty much just like plugging into the wall direct.
Surge protectors offer some level of protection against power spikes. How much and how well varies considerably.
Surge protectors offer protection in amounts called joules. Think of this like a reservoir of protection. If a product has 1,000 joules of protection, that means it can take ten 100 joule hits, or one 1,000 joule hit. Generally, the more joules the better.
Most surge protectors are trigger designed, when they sense a surge on the line they cut power by triggering a fuse.
How do you know how many joules a protectors has left, or if the rating is even accurate? Well, you don't. The Wirecutter did a massive test on surge protectors
, essentially blowing them up to see how well they worked, to see if they could answer this question.