Dunno what they are actually called (and I refuse to look it up) but I always called those 6 pin and 8 pin power connectors and people seem to know what I mean.
Hasn't really been an issue in the last 20 years for me and now those are really only used for the CPU power and AMD GPUs. Also aren't those curved pin cover things there specifically so you couldn't plug it into the wrong thing?
Oh yea, don't mix and match PSU cables, that's pretty common knowledge, just use the cables that come with the PSU and you're fine though. The adapter on the picture used to be pretty common and came with the PSU before modular PSUs became the norm though, not really used anymore from what I have seen.