Out of most of the electronics I use, I have two, both of them speakers, that use a power adapter that simply steps down the voltage without rectifying it. Why did the designers choose to put the rectification circuitry in the speaker instead of the power adapter?
Electronic – Why do some power adapters output an AC voltage
acdcpower supply
Best Answer
One reason is that you usually need positive and negative voltage for audio amplifier. (Like +5, 0, -5 V).
Another reason: Some devices run directly on AC, e.g. Christmas light bulbs can do.
Yet another reason: Some devices need two different voltages, like 5 V and 12 V.
Yet another reason: An external step down transformer provides just safety. Voltages no higher than 50 V are usually accepted as safe (although not very safe with high current). So the transformer makes it safe, the rest is in the device.