If you a trying to boot your rpi5 from an usb ssd and your fans turn on, then the rpi5 turns off, the issue might be the fans, they draw too much power. I had now idea about this issue, since when i bought the rpi5, i bought a case with fans that apparently don’t draw so much power, so i had no issue until i decided to switch to the original fans, then suddenly but also randomly my system would shutdown, a few second after starting up. After many hours of debugging, and a lot of trial and error, i found that the actual problem was the fans. So i switched back to my older fans, and now the rpi5 works again, and boots from the usb ssd with no problem. In case you want the same fans, mine are called “Heatsink Case for Raspberry Pi 5 Black Color, Dual Fan”.
So why the trouble, I have a “AI Kit M.2 HAT+Hailo Al Acceleration Module” that does not fit very well with may heatsink case, and also I bought the new Raspberry Pi AI HAT+ with 26 TOPS, so I wanted to streamline the setup, so I have changed my dual fans with the official, much small fan, that would let the AI hat sit nicely on top, then all the problems started, since I also wanted the rpi5 to use ssd for it’s OS system, since i will be using the AI stuff I want the speed that the ssd brings.
Anyhow, switching back fixed the problem, so in case you want the usb ssd boot to work, i suggest different fans 🙂