I have my pi, installed with the pi os on an SD card and I have the yellow inkywHAT display. I have a standard display plugged in at present. I am trying to attach the display to the pi using the thick black cable that came with it.
When I attach the inky whilst the pi is turned on, the pi turns off.
With the inky plugged in and the pi off, the pi does not switch on.
First off, I wouldn’t plug anything like a Hat or pHat onto the GPIO while the Pi is powered up. There is a good chance of damaging something.
What model Pi, and what are you using for a power supply? The current rating of the supply may be important.
I tried first by plugging it in whilst powered off, and then trying to turn it on, with that failing, I thought I should try it whilst it was powered on. That failed also.
I am using a 24W 2-port Anker usb charger with a power cable.
Using a “battery charger” as a “power supply” is IMHO a bad idea. They usually have poor voltage regulation and don’t maintain the solid +5V the PI wants to work reliably.