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Sorry Not Really A Computer Question, But Its The Closest Section I Could Find To This Question.
Basically I bought a clock radio which can also wirelessly charge my phone, but it is powered by a USB cable.
So my socket on the wall in my bedroom has the two traditional sockets, and two USB sockets all in the one back plate. I installed this a few years ago to cut out the need for extra plugs, ie USB plugs.
But for some reason if I plug the clock radio into the built in socket on my wall, it won't power up, yet other things will from that port, so I know its working.
Yet if I plug in a USB plug, and then plug the clock radio into that it works fine.
So are there variable volts for various different USB plugs/sockets?
I just assumed USB stood for Universal Seriel Bus, but I thought Universal in the sence its one size for all.
But am I wrong?
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One size may fit all but the voltage needed to power the device varies. If you plug a USB into a normal plug that comes with the device then that plug will have the correct transformer inside it so that the 240 volt mains will be stepped down to what the clock radio needs which will be more than the default of 5 volts. Look at the back of the clock radio and it will probably more like 10-12 volts so the clock radio can function and also have a USB output from which other things can be plugged.
All USB Type-A ports provide 5V DC. However the maximum current available through such ports can vary. I suspect that the built-in socket has a relatively low current rating, meaning that there's not enough power for the clock radio. The USB-adapter plug though offers a higher current, enabling it to provide power to the lock radio.
"but am I wrong to expect the very idea of those back sockets we're to deter the user for the need for extra plugs," - that was not the idea. The idea is it's a normal plug and also a USB output. Most phones come with those little 3 pin plug device and you can plug those in to the main socket and charge at up to 20v but if you don't have one, you can still plug the USB lead into the USB and get 5 volts, slower but still charging. That's the idea
How old is the wall socket with the USB chargers built-in? A few years ago the only things that charged from a USB socket were phones, so it could be that yours was designed with this in mind and has only a low wattage output. Nowadays lots of things are charged via USB and the power sockets are providing more current. A radio takes quite a lot of power (compared to a phone) so it is quite possible that the mains/USB socket just isn't "man" enough to power yours, where the separate adapter you have is.
Thing have moved on a lot since the original 5V USB standard; the USB Power Delivery standard allows for USB voltages up to 48V and power to 240W (48V @ 5A).
Such increased Power Delivery voltages use USB-C connections, with the connected device signalling the host to provide the required power.
But not all USB-C configured mains powered adapters (or hosts) are configured to deliver this higher power (Power Delivery).
So a device with a USB-C power socket may not work if it requires more than 5V and is plugged into a source/host only capable of supplying 5V.
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