You can't check by serial number or model number, because counterfeit devices can also counterfeit (lie) about the model number. The only way to be sure is to buy the device from an Apple store or an Apple authorized reseller. Or get one of the many quality 3rd party USB power sources if that's what you are talking about.
BTW, do you mean the thingy that plugs into the wall, or the cable that connects the thingy that plugs into the wall to your phone? Neither are "chargers" - the charge is built into the phone. These devices are just a source of USB power and a cable to get the power to your phone.