USB 2.0 -laitteen lataus nopeutuu, jos se liitetään USB 3.0 -porttiin?

Do USB 2.0 devices charge faster if they are plugged into a USB 3.0 port rather than a USB 2.0 one? I am not asking about a specific device, I just mean in general.

I know that a USB 2.0 port can provide 500mA and a USB 3.0 port up to 900mA, but is a USB 2.0 device able to draw the extra power possible via the USB 3.0 port and charge at 900mA, or will it only draw up to 500mA and nothing more?

Shorter Answer

Do USB 2.0 devices charge faster if they are plugged into a USB 3.0 port rather than a USB 2.0 one? I am not asking about a specific device, I just mean in general.

Yes, no, and maybe is the answer. While you are asking this question as a general, non-device specific question, the reality is it is completely device dependent; nothing will take on more power than it is designed for and will limit its intake to what it needs even if given more power. More details below.

Longer Answer

I know that a USB 2.0 port can provide 500mA and a USB 3.0 port up to 900mA, but is a USB 2.0 device able to draw the extra power possible via the USB 3.0 port and charge at 900mA, or will it only draw up to 500mA and nothing more?

It takes two to make it work. The power source and the device it powers.

It is a two-way street in the world of charging; how much the power source is willing to give and how much the charging device is willing to take. It is completely dependent on the charging circuitry of the device itself. One could say that a USB 3.0 port has the potential to charge a device faster than a USB 2.0 port, but if the device itself is not designed to handle increased power output, it will just grab power at the rate it is specifically designed for.

Charging an iPhone with an iPad charger provides results dependent on the iPhone model.

While this example is basically based on the USB 1.1/2.0 power output model, the overall concept of “power input/output depends on the device” is still the same. Just look at this video where a user does what many people have similarly tried to do in the Apple device world with different iPhone models; attempting to get an iPhone 5 to charge faster by using an iPad 4 12W/2.4A charger (iPhones typically come with a 5W/1A charger). The end result in the video is that it shows an iPhone 5 is only going to charge at the rate it is specced for (only 1A draw).

Do take into account that the video linked above is relevant for iPhone models 5s and lower. It turns out, according to this video, that the iPhone 6 and 6s can accommodate more power flowing to them, so instead of drawing the standard 1A when connected to the iPad charger, they can draw between 1.2A to 1.3A. A nice little speedup in charging.

The USB 3.0 Power Specification

As far as USB 3.0 power output potential is concerned (according to the USB 3.0 power delivery specification), this is the potential wattage output for USB 3.0 connectors:

• Profile 1: 5V @ 2A (10W)
• Profile 2: 5V @ 2A, 12V @ 1.5A (18W)
• Profile 3: 5V @ 2A, 12V @ 3A (36W)
• Profile 4: 5V @ 2A, 12V, 20V @ 3A (60W)
• Profile 5: 5V @ 2A, 12V, 20V @ 5A (100W)

Looking at that spec, it seems like you can power most anything in the world with USB 3.0! Hooray! Throw out all those proprietary chargers. But wait and look again. That power potential is all dependent on the device you wish to connect and power with USB 3.0. As the spec states, it requires new cables; all must be USB 3.0 for power requirements greater than 1.5A or greater than 5V. So you cannot expect to just plug a basic USB 1.1/2.0 cable into a USB 3.0 port and get more power out of the setup.

The USB 3.0 Cable Specification

Also, the USB cable itself only plays a role when using USB 3.0 capable devices which can then negotiate the USB 3.0 power spec. USB 1.1/2.0 cables have four leads while USB 3.0 cables have eight leads. Here is a nice chart that shows you how USB 3.0 cables differ from USB 1.1/2.0 cables: