Question and suggestion: FLM and power supply near DIN rail is a tricky thing when there is not enough space in the switchbox. While the FLM02 can easily be run from a DIN rail 12V power supply with own fuse, of course, the AC supply is a little more tricky on the FLM03.
Would it be possible to run the FLM03 also from a bell transformer? These are available in DIN rail housing and with 8V standard they should be near enough to FLM requirements.
Possible? I will surely test it to clean up the mess with all the wall warts...
Yes with the appropriate electronic behind the transformer: bridge rectifier, capacitor, linear voltage regulator 7809 or 7812. But this is not very efficient for your power use. Better use a 12v switching power supply @1 amp.
But, i don't know on what voltage the FLM03 runs.
Well Fluc, you didn't get the question correctly; surely with DC you can do this - and linear voltage regulators are "last century" as there are more efficient ones as you write yourself (and to drive HAMs crazy). The question is to use a DIN-rail variant as replacement for the AC (sic) supply also providing means for voltage and voltage phase measurement. As the measurement itself is "just software", the potentially different supply voltage to the original power supply should be able to be parameterized. For power (sic) supply, the voltage is irrelevant as long as it reaches the internal demand of the FLM.
See, what the FLM03 is capable of https://github.com/gebhardm/flm03/tree/main/MQTTrealtime