A batch of 1.3 inch white I²C OLED displays arrived from halfway around the planet, so I figured I could run a quick acceptance test by popping them into the socket on the crystal tester proto board:
The first one flat-out didn’t work, as in not at all. The original display continued to work fine, so I compared the old & new displays:
Yup, swapped VCC and GND pins. I should be used to that by now.
I rewired the socket, tried the new displays, undid the change, popped the original display in place, and all is right with the world. Somewhat to my surprise, all five new displays worked, including the one I’d insulted with reversed power.