Tarnishing

What sits on the plate?
If the plate sits in the cleaning solution it could very well be a cathodic process. (cathode and anodes are poles of a battery)

Silver tarnish is, after all, an oxidation layer that is the result of some form of half cell reaction (same as rust) so cleaning would either be the result of either abrasion (scrubbing) or a electrodisposition (aka rust). Since these cleaners advertise themselves as 'effort free' I'd say they use electrodisposition which means that they introduce some material that has a greater oxidation potential than silver, that reverses the silver tarnishing half cell reaction through a conducting solution.

BTW this is the same reason you attach a zinc block to household plumbing, the zinc is more reactive than either iron or copper. If the zinc block is connected to the metal plumbing with a conductor, the zinc will sacrifically protect the rest of the system from rust.

There is a similar process where you can introduce an electrical current to counteract the half cell reaction instead of using a sacrificial material. This process also raises the potential above the half cell. This is effectively what you are doing when your charging a lead acid battery.

Rap