I think you mean a "surge protector" which protects your PC gear from electrical spikes and surges.
There are cheap ones and more expensive ones.
No way of knowing if they work until a surge or spike actually occurs without damaging your PC.
All I can tell you is that none of my gear has suffered during an electrical storm (of which there have been several this year).
Before I started using a surge-protector there was a violent electrical storm which killed my computer's NIC, so I can personally say that my surge-protector seems to be living up to the manufacturer's claims.
The bottom line is it's always best to use one in my opinion, they are not just a gimmick.
But get a good quality one. My current one is a Belkin brand plug-in type with a power socket and protection LED on the front face.
Cost me around £30 two years ago from Amazon.