Well I decided to take Etronix charger back to where I bought it from just to run it passed those guys and see what they thought.
Right off the bat they said the only ones they got back were ones that had issues with soldering of the mains cable jack to the circuit board. They said that they knew of a customer who re-soldered it and was fine from there on out.
To check the theory they plugged in a 12 volt power supply and it powered up straight away. So I took it home to have a go at re-soldering it.
What I found was two separate circuit boards, one for the charger itself and one for converting the 250 volt AC power to 12 volt DC. I checked the soldering of the mains plug jack and the soldering to the circuit board. All looks fine and multimeter confirms 250 volts going to the circuit board. I also can confirm 250 volts going to the first fuse and what I think is a resistor... after that I have no idea. What I can confirm though is no power running from the end of that board to the charger's main circuit board. So apparently the inboard power supply/converter is the problem. Not surprised because you can clearly see a notable difference in quality between the two circuit boards.
Now, my question is this. Armed with this new knowledge, would it be better to purchase a quality power supply instead of a new charger that could potentially have the same problem?