Not really pissed off, but rather annoyed me a bit...
There is this one children play-kitchen by Ikea, called DUKTIG:http://www.ikea.com/de/de/catalog/products/S49874533/
This one uses a battery powered fake ceran stove that needs 6x AA batteries. I was like "it's 9Volt, why not create an adapter so that it won't waste batteries".
So I tried alligator clamps and a 9Volt battery. Turned out, that it didn't work. I opened up this ceran stove (it's easily dismantable), took a closer look. Realized that it should work in theory: an IC for switching on each cooking area separately, a couple of capacitors and resistors and rectifiers...
Then it dawned on me... why did this system need two positives and only one negative?
Well... they created a some sort of parallel bus system. One 9Volt battery alone doesn't produce enough juice to get that thing to run. But having several basic 500mA batteries in parallel (actually 2 AA in parallel to 6 in series, with only 6 batteries) - so that should be around 1-2A if I'm not mistaken). On top of the ampere usage (again, if I'm not mistaken), the system actually pics up at the 3V point (running through 2 AA's from one global negative to the first postive pick up point) and the 9V point (running through six batteries from global negative to the second postive pick up point) rather than one single 9V.
Interesting, but creating an adapter for a 9Volt battery or even an external PSU would be a PITA and so not worth it.
At least I got that whole thing (the lower half of this children kitchen) for free due to a clear-out session. So I won't critisize... just annoyed me a bit that I couldn't McGuyver an adapter or something.