"Eigenvector"
But look how they work. Like an alligator clamp.

If several outlets are daisy-chained, the final current draw on the first
plug-in may be significant - and greater than the miniscule contact area
can handle. This results in charring, overheating, and (if you're lucky)
loss of connectivity.

I've never seen how they're constructed internally, so I can't say
anything for sure. But it seems like losses in a circuit due to bad
connections would be measurable and testable.

Go to HD and buy a cheapo outlet with push-in connectors ($0.39). Whack it
with a hammer.

Now you can see the miniature speed-nut that is the electrical connection.

Put 15 Amps through that teeny surface area and you've got molten brass.