I recently found out something interesting about MC4 connectors for solar panels. It turns out the only legitimate MC4 connectors are manufactured by Stäubli. Every other MC4 connector you see is a clone of the originals, which is dangerous if they are mixed (a male of one vendor, a female of another). Differences in tolerance/fit can create unstable connections which can cause overheating, arcing, even fire. So Stäubli posts pictures so you can try to identify the clones (the easiest giveaway is Stäubli's O-rings are always black). It's such an issue that standards now require you to acquire connectors from one origin, and use the same brand and type. But I think a lot of consumers are buying random solar gear now and just plug in whatever connectors look like they fit together.