Measurements don't make sense

Welcome, Mats, to the OEM forum.

Have you loaded the sketch for 3-phase systems?

The sketch that is loaded when you receive your emonTx will be for the UK single phase system. If you have not changed it, then the phase with the a.c adapter should be correct, the other two will probably be negative and showing approximately half of what you expect.
If you download the zip file from this link, you will have the full documentation and installation instructions as a PDF file.

You will need to install the Arduino IDE to configure and compile the new sketch, and to load it into your emonTx you will need a programmer.