… it is way too much overkill since it supplies 120v which you then downsize to say 5v (which wastes a lot of energy).
Transformers in general, and specifically the one in an Apple iPad-charging "wall wart" wastes VERY little energy. As evidenced by the fact that that it gets only a little bit warmer than ambient temperature.
The reason is that they are not transformers but switched mode power supply which use an electronic circuit to do conversion and step down.
PKS
I didn't really want to get into that much technical detail, but…
From the Wikipedia article:
A switched-mode power supply is an electronic power supply that incorporates a switching regulator to convert electrical power efficiently. Like other power supplies, an SMPS transfers power from a source, like mains power, to a load, such as a personal computer, while converting voltage and current characteristics. Unlike a linear power supply, the pass transistor of a switching-mode supply continually switches between low-dissipation, full-on and full-off states, and spends very little time in the high dissipation transitions, which minimizes wasted energy. Ideally, a switched-mode power supply dissipates no power. Voltage regulation is achieved by varying the ratio of on-to-off time. In contrast, a linear power supply regulates the output voltage by continually dissipating power in the pass transistor. This higher power conversion efficiency is an important advantage of a switched-mode power supply.
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Posted by: Jim Saklad <jimdoc@icloud.com>
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