I encountered a weird behaviour for me with my very first Raspberry PI (version 4 with 4 Gb RAM). I purchased it from an official French supplier along with a dedicated power supply (OKDO branding for the two) and a Waveshare LCD touch screen.
Like a negligent beginner
, I set up everything before testing the card solely thus I spent a lot of time investigating possible issues on a lot of others things (LCD screen, HDMI, config.txt, SD card, Raspbian image) but it was highly instructive 
.So lacking a solution with the supplier support, I started to pay attention to these LED lights with in particular the green ACT that wasn't blinking. Consequently I tried to restore the bootloader but without more success
.Finally after a good night's rest and just before sending back the RPI to the supplier, I made a last test and for whatever reason (probably weariness) I plugged the power socket first and then the USB-C port and... WTF
the green LED was blinking as expected. Obviously it took me some extra time and other tries to exactly figure out how I managed to get the RPI booting at this moment and not previously.Now I found that the official documentation mentions this procedure to set up the card power ... Well I really doubt I'm the first who fell into this trap if this instruction is something other than a precaution. Wouldn't have an issue with my card or the power supply
