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On many (if not all) of my wall charger it says:

INPUT: 100-240V / 0.5A
OUTPUT: 5V / 2A

So, according to my poor knowledge this would mean that the input power is 50-120 W and output power 10 W. But this cannot be right as the efficiency would be super low?

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It is to help allocating how much you can connect to a power strip or after a fuse, so that fuse does not trip when plugging devices in or flipping a switch on, as the initial surge current is higher than operating current. Chargers generally are quite efficient so when 10 Watts goes to phone, the charger could take 12W maybe in, if it takes 20W then it is a pretty stupid charger. Some parts of the world like California have pretty strict rules how much devices are allowed to waste energy.

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It could still be true, because some power converters are very inefficient (there are even converters who only lower the voltage, without resulting in any current gain).

10 W is not so much, so it will not cost a lot of (wasted) energy anyways.

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  • \$\begingroup\$ Yeah, but if it takes 120 W from the wall and you have, let's say, 5 devices charging. Then it would be 600 W. I have an extension cord with 8 sockets + 2 integrated chargers. \$\endgroup\$ – juzzlin May 31 '19 at 8:32
  • \$\begingroup\$ @juzzlin Where do you get 600 W from? \$\endgroup\$ – Daniel Tork May 31 '19 at 8:41
  • \$\begingroup\$ @DanielTork Probably from 240 V * 0.45 A * 5 devices = 600 W \$\endgroup\$ – Michel Keijzers May 31 '19 at 8:47
  • \$\begingroup\$ So "it is not so much"... But consider that most people leave the chargers plugged in even when the phone is not connected (usual excuse - I will loose it...) then say at 1W multiplied by the number of phones in the country means that it is one power station or more for wasted energy.... \$\endgroup\$ – Solar Mike May 31 '19 at 9:11
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    \$\begingroup\$ When nothing is attached, it will not use energy (or maybe a very small amount in case a LED is part of the circuit). The 0.45A is the maximum. \$\endgroup\$ – Michel Keijzers May 31 '19 at 9:23

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