Note: this is not about a specific device but the general aspects of charging a USB device using accessories with different USB standards so I hope this fits here.

I've got a Samsung Galaxy Smartphone with a USB 2.0 Type C charging port.

Using the stock Samsung wall plug (9 V, 1.7 A output or 5 V, 2 A fall-back) and charging cable (USB A to C) the device gets charged utilizing Samsung's "adaptive fast charging" technology.

Using the included charging cable with a generic USB A wall plug without Power Delivery (5 V, 2 A output) nets a very slow charging speed of approx. 900 mA. Incidentally the same current as specified for USB 3.0 ports.

The same exact charger and a regular Micro USB cable would charge any old smartphone with a maximum of 2A sans utilizing USB-PD. Why doesn't it work with the OEM Samsung USB A-to-C cable? The USB 2.0 specification also states a maximum of 500 mA and every charger in the last years exceeded that. The Samsung device doesn't even have a USB 3.0 port, it's just USB 2.0 with a Type C connector.

I'm trying to understand this from a technical viewpoint. Can you point me into the right direction? USB 3.0+ and Type C is honestly pretty confusing.


USB Type C is simply the connector - the protocol in use is USB 3.X. Of course, it affects the connector, but the limitation is in the phones support of 2.0 and not because its a type C connector.

Also, AFAIK Samsungs "adaptive fast charge" actually uses Qualcomms solution of delivering a 9V load instead - this is then converted at the phones side. VOOC (or oneplus Dash) charging works with current only, this is where you may get confused. I think the device should still take 2 Amps, but it may be device limited to work only with samsung fast chargers - for safety or for exclusivity, maybe both.

If you see Oneplus cables, they are comparably quite thick - this is to support the thicker wires, which of course are needed for the 4 amps sent to the phone. Your cable might not be thick enough to support the larger currents - try another USB-C cable if you can, one that's preferably rated at a larger current. The included cable is good for 9V at a lower current, but may not support currents larger than the fallback of 2.0A. That's why its recommended to try different chargers. cables, etc. Also, to make it a fair test, try and let the battery discharge to somehting like 20% - so that the device isn't software limited the charge! (It reduces it to scale of milliamps at 80% to protect the battery)

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  • Thanks. Is the protocol in use USB 3.x though? Type C is not limited to any protocol and the Samsung smartphones are shipped with USB 2.0 peripherals. That's where my confusion stems from. I'll try a different cable though. – pomeloy Jan 9 '19 at 19:31
  • @YoungUn I think that USB 3.X uses 5 extra pins (see any SS (usb3.x) port, you'll see the 5 small pins before the 4 main ones) so it can send a larger current, as well as data. Because of this though, both the power adapter (or computer), cable, AND device have to be USB 3.X compatible. Essentially, the protocol is as high as the lowest component - the device and adapters need the extra pins, and the cable needs the extra wires for it. However, the smartphone might actually support USB 3.X,though I'm not sure it can make use of larger currents, you might have to look at the official documents – QuickishFM Jan 9 '19 at 20:07
  • The cable in question is a USB 2.0 cable without these extra pins. – pomeloy Jan 13 '19 at 16:40
  • Yeah, so I'm guessing it defaults to USB 2.0 then. The benefits of USB 3 are harnessed using the extra pins for power delivery and data, so if they aren't connected then the system uses 2.0 as standard. – QuickishFM Jan 13 '19 at 16:45

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