You can release and remove the plate by pulling at the handle:
Then this plate is attached to the PSU:
And the whole arrangement goes into the case:
The purpose of this all is a mystery, however. The developers designed the PSU container in such a way that it can only be installed from the outside and had to invent the adapter plate for that purpose, but they might have made a normal fastening mechanism that would allow to install the PSU from the inside. This looks as if the developers took some solutions from server cases without thinking much whether they would do for a consumer case at all.
We’ve got no complaints about the installation of the mainboard and expansion cards. Just don’t forget to connect power and interface cables to the HDD cage:
These connectors become blocked afterwards by the installed fan:
The screw-less locks for expansion cards do their job quite well:
No problems with them, and the locking pressure is normal. The problems arose with the HDD cage, or rather with the box for its fan. Our graphics card nearly was nearly touching it: