If we take into account all the generic types, the number of different connectors on the market will be gigantic. They differ in appearance and manufacturers, but it is rarely important to the end user. What does matter is compliance with standards, compatibility with other types and whether these mixed connections meet all relevant requirements.
Virtually all solar panels that are sold today will have solar connectors that meet all relevant regulations. However, if you’re buying used modules, inquire about the type of connectors the panels feature. MC3 connectors, for instance, are weatherproof and look fairly reliable, but the absence of a positive locking mechanism prevents them from being NEC compliant. It means that they can’t be used for connecting solar panels in most states.
Another important topic is the combination of different connector types. Compatibility is rarely an issue, because most generics are intermatable with MC4 connectors. The problem is that many of these connections do not comply with all relevant standards. Still, some do. For example, the T4 connector made by Canadian Solar. The company released a document
confirming recognition of T4 and MC4 connections. In all other cases you can either choose to stick with the same connector type throughout your system or contact the manufacturer to request a warranty addendum and replace them.