I also have a keyed 40 pin cable from Amazon:
GPIO Ribbon Cable for Raspberry Pi Male to Female 40pin Breadboard Jumper Wire Computer
After connecting the cable to reTerminal I compared the orientation to a Raspberry Pi pinout drawing and then tested the 5V, 3V and GND pin with my Volt Ohm meter and they were as expected. I did not add any other adapters or connecters.