[jan-jaap]

This may be a silly question, but how do you remove the PSU+bracket from the system?  I can find 4 screws on the top of the power supply board, and then 2 screws behind it from the other side but it seems those screws may be removing the board from the bracket.

You don't touch the screws of the PSU PCB because they attach it to the bracket. You release the PSU PCB + bracket from the PI chassis by unscrewing 4 screws from the side of the E-module. You need to remove the E-module first. This is what the back side of the PSU bracket looks like (the side facing the divider with the E-module):



You can see the four screw holes, and if you look carefully you'll see a couple of hex holes where the mounting studs of the PCB are pressed into the bracket.

Removing the bracket + PSU from the IRIS chassis can be a little fiddly. You have the impression it's too big to remove. I assure you it fits, but only just.

NB: also visiible in this photo: the brown "jumper cable" to start this PSU outside the IRIS. This where the power switch normally connects.