New Pi 3B+, Sandisk Cruzer 16GB as adviced here: https://www.raspberrypi.org/blog/pi-3-booting-part-i-usb-mass-storage-boot/
Formatted as one fat32 partition then Etcher:ed with the lite version, both as zip and as the img (made no difference). Plug into Pi and then plug in power: red power light comes on, the green doesn't even flash once. Tried a Corsair 8GB USB stick - same thing. The blue power led on the Corsair flashes but the green act light on the Pi does not.
It works when the same image is Etcher:ed onto an SD card, the green light blinks some on boot and there's video out and the OS boots.
Did "v cgencmd otp_dump | grep 17: " and it's already 3020000a as the official documentation says it should be (meaning it is set by default to be able to boot from a USB drive)
(lsusb lists the Corsair USB drive as a Corsair keyboard..but the Sandisk Cruzer appears detected properly).
I even tried the last bit in the official documentation - put bootcode.bin unto a fat32 formatted SD card and connect it as well as a USB mem and then power on: Three or for quick flashes in succession. ('general boot failure' or 'start*.elf not found')
My power supply is a Pi logo:d one, "Stontronics', 5.1V 2.5A (should be the official one). It powered a 3B for five months.
What am I missing here?