I recently acquired a toy that uses this transformer: 
but since I live in a 220V area, I cannot use it directly.
I have this generic AC-DC adapter:
which in theory is all I need because it has a 4.5V output and enough amperage.
However, I'm a bit concerned since when measuring the voltage of the ac-dc adapter when it's set to 4.5V output, I get ~10.5V. I know that the voltage measured in a no-load scenario is supposed to be higher than when it actually has load, but it seems a little bit too much.
When set to 9V, it outputs ~16.6V
Is it safe to use this ac-dc adapter with this toy? Or it might be broken and supply more volts than it indicates?
Answer
This is one of the hazards of trying to use a greatly overrated (3:1) unregulated supply. That's actually the first time I've seen a no-load voltage specified on the label, very handy. Yes, it could potentially damage the toy.
You could try the adapter on the 3V setting and see if the product works, but it might be a bit on the low side.
Another possibility is to add a dummy load to the universal adapter (something like 10-15 ohms 5-10W), but it might get very hot. Or you could poke around and find a ~300mA 4.5V adapter that can accept your mains voltage.
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