Bear in mind that if you’re using those to power the emonTx, the no-load voltage needs to be about the same, viz. 12.0 Volts ±5%. “9 V” refers to the output voltage at full load, it is very lightly loaded by the emonTx. And the regulation is important too, because if the source impedance as seen by the emonTx is too great, there’s going to be a big dent in the wave where it draws its chunk of power on each cycle, spoiling the voltage measurement.
As neither of these parameters are mentioned (nor can be inferred) from the data in that link, caveat emptor.