The first thing I noticed with the ETX70 was that the batteries would run out quickly and the scope would do all sorts of weird things.
There were no ETX70 power supplies available at that time, so I hunted around for a suitable transformer.
I eventually found one in my local Dick Smith store – Catalogue No. M 9630 Multi Voltage Regulated DC Supply.
This has 3, 6, 9 and 12 volt output (only the 9v concerns us!). It is regulated so the supply is a constant 9 volts (didn’t wanna take chances!). The current rating of 0.9 amps is ample (pardon the pun) when I checked the ETX current draw under load. Input is 240 volts (good for me in Australia) and price was AU$46.93.
All that was left to do was to connect a suitable wire and 9volt battery clip (careful with the polarity!). The ETX battery compartment has a handy notch that the wire fits through and the 2 small cable joiners I used serve as a stopper to prevent tension on the battery clip.
Have since seen commercially available products recently - as long as they are specifically for the ETX70 they should be ok - See accessories section.