Weird USB cable (usage?)

3 years ago I went volunteering and brought back this weird USB cable and in those 3 years i never could figure out how to use this USB cable and what is the purpose of its disposition. So... what do you use this cable for (I think those are 3 USB 2.0 connectors - I don't know how to differenciate USB 2.0 and older USB's...) ?

Answer

What is this weird USB cable

The cable is called a USB Y-Cable. It is designed for devices which require more power than is available from a single USB port.

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What are the 2 different kinds of Y-Cable?

• One male connector, two female connectors

  
  

  There are two types of the one male two female cables. One is a basic charging cable, splitting one port's
  power across two devices. The other is a specialised cable that
  somehow splits the data lines - and it's only used in very specific
  applications.




• Two male connectors, one male or one female connector

  
  

  What happens is you have your USB cable, one side for the host and
  one for the device, but with an extra connector attached. This extra
  connector does not have any data lines (D-, D+); it only has the power
  lines (GND, VBUS). It's attached in parallel to the existing cable. In
  other words, VBUS is connected to VBUS and GND is connected to GND.

Source Can I safely connect the power-only-end of a USB-Y cable to an other power source? answer by Bob)

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So what is this weird Y-Cable?

The extra power plug is sometimes a double-sided plug, with both male and female.

It's a pass-through so that extra port used isn't totally wasted.

The female connector on the back of the plug allows a low-current device to use the second port.

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Power requirements

Some devices, such as high-speed external disk drives, require more
than 500 mA of current[89] and therefore may have power issues if
powered from just one USB 2.0 port: erratic function, failure to
function, or overloading/damaging the port.

Such devices may come with
an external power source or a Y-shaped cable that has two USB
connectors (one for power and data, the other for power only) to plug
into a computer. With such a cable, a device can draw power from two
USB ports simultaneously. However, USB compliance specification
states that "use of a 'Y' cable (a cable with two A-plugs) is
prohibited on any USB peripheral", meaning that "if a USB peripheral
requires more power than allowed by the USB specification to which it
is designed, then it must be self-powered."

Source USB