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The volts MUST match exactly, the polarity MUST match exactly, and the milliamps MUST be the same or more. The unit will use what it needs, even if to much is being offered. On the other hand, too few milliamps will BURN THE UNIT OUT!

So on top of loosing your equipment, you could loose your life also ... since it is a major fire hazard!

Clearly the voltage is not the same. The phone needs 7V, the charger is at 9V. Mismatching voltage will not work.

Using a power supply with a maximum current rated below what is required will result in 1) the supply voltage dropping, and 2) the device generating additional heat. Such low power requirements do not present a serious hazard, fire or otherwise. However, the higher voltage will likely seriously damage the phone. Had the supply you chose been rated at 7V 400mA, the phone would likely still charge, albeit much more slowly.

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โˆ™ 2015-07-15 19:43:04
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Q: If a phone needs a 7v 900ma charger can you use a 9v 400ma if the voltage and polarity are the same?
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