Since the power specification for USB 3 is significantly higher than that for USB 2, I'm wondering if it's important to choose a powered USB 3 hub over a less-expensive unpowered USB 3 hub.

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    It depends on the power requirements of the devices you will be connecting to the USB Hub.
    – Ramhound
    Feb 21, 2017 at 18:01
  • seems there are some computers with extra high power usb ports superuser.com/questions/690074/… that can go up to 5A though i'm no expert
    – barlop
    Feb 21, 2017 at 21:05

3 Answers 3


I would strongly advise not to use any unpowered USB hubs (officially called "bus-powered hubs", and sometimes advertised as "mobile hubs") if you don't want communication/connect surprises, for the following reasons:

  1. A bus-powered (aka "unpowered") USB hub cannot officially supply full power to downstream ports, because the power source is already limited to one-port standard USB capability, minus the hub own IC power consumption (which is about 1W or 200 mA in today’s technology). This leaves about 700 mA to all downstream ports. Since the system must reserve 150mA minimum to each port, it leaves only 250 mA maximum for a 4-port hub, see Sec. 10-14 p.10-61. This power budgeting is new and improved over USB 2.0 specifications, where 100 mA was hard limit, no balancing.
  2. In theory, a bus-powered hub must advertise its power source in hub configuration descriptor. USB system software will then apply power policy and refuse to connect any USB device when the power budget is depleted. This is very inconvenient for ordinary users, so unscrupulous manufacturers are cheating. They lie in hub descriptor by setting it as "self-powered" (i.e. using external power source) no matter what. Since these “mobile hubs” cannot be USB-IF certified at all, they usually have several other out-of-control deficiencies, and who knows what else.
  3. One fundamental deficiency is that these cheap hubs don’t implement VBUS power off function. Even if all ports can be ganged and presumed to serve as “charging ports”, the VBUS toggle function should be implemented to signal to downstream devices when upstream hub connection to host starts running. See Sec. of USB 3.1 specifications.
  4. The other typical issue with cheap hubs is huge excess of capacitance on VBUS. The USB requires no more than 10 uF of load to upstream VBUS. Most cheap hubs use a common VBUS rail, but connect huge caps to each port. For example, the TP-LINK “mobile hub” Model UH400 has a 220uF cap per port, making the upstream VBUS loaded with lumped cap of 880uF, exceeding specifications by a factor of 88X. This cap can easily break any PC on connect, by nearly shorting +5V standby rail.

The bus-powered cheaply-implemented USB hubs are mostly good only for connecting mice and keyboards, and maybe one cheap pen drive. The newer Type-C connector and PD (power delivery) specifications might change this power balance picture, but the main USB specifications are not aware of this, and system software guidance is lacking for this case. And Type-C with PD won't be cheap by any means. Having a self-powered USB hub removes a lot of headache from USB interoperability standpoint.


Most USB hubs can just draw current from the computer itself. Keep in mind that a computer's USB 2.0 port can normally supply only 5V @ 500mA so if you try to draw more current than that you will probably need the power supply even if your hub is USB 3.0 .

If your computer is USB 3 ready you might get up to 900mA for data transfer and on dedicated charging ports you will get up to 3000mA with no data transfer.

  • To be clear, I refer to USB 2.0. However, USB 3.0 can indeed draw up to 3100mA Feb 21, 2017 at 19:35
  • Well then you should edit your answer and put that in. Don't leave an answer with misleading or wrong information in it that is only corrected in a comment.
    – barlop
    Feb 21, 2017 at 20:59
  • Also your answer as it stands, is less accurate than the question.. The question at least mentinoed USB3. Also according to superuser.com/questions/690074/… USB3 is 900mA though you say it's 3100mA
    – barlop
    Feb 21, 2017 at 21:07
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    However USB 3 is indeed capable of 3.1A for dedicated charging ports, and 3.1 with USB type C actually relies on this current. Feb 21, 2017 at 21:59
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    @unknownSPY, Type-C can handle 5A only if cables are equipped with e-Markers, and the port supports corresponding elements of Power Delivery. If no PD, the Type-C can advertise only 3A max (10k pullup), and if the port is the standard Type-A, the 900 mA is an official maximum. Keep in mind that Type-A connectors are maxed at 1.5A contact rating, and only special "power delivery" ones are rated at 2.5A. Feb 22, 2017 at 22:14

It all depends on what you are connecting to it. If you are just using usb flash drives or DVD drives or mouse/keyboard you should be ok with unpowered.

But if you want stuff to charge from it with any speed (like a phone etc) or if you want to connect 3.5" hard drives or other higher power demanding peripherals to work you need a powered hub.

  • Just to make things explicit. DVD or CD burners also fall into the high power range (about 1.2Amp @ 12v). A DVD drive might be fine. A DVD burner might burn things out.
    – Hennes
    Feb 21, 2017 at 18:40
  • unknown: Why do you say DVD drives should be OK with an unpowered hub?
    – barlop
    Feb 21, 2017 at 21:02
  • @barlop because I use a blu ray drive with an unpowered dock every day, no issues
    – unknownSPY
    Feb 21, 2017 at 22:04
  • It all depends on what is inside the host port. Some ports might be designed to supply 5 A or more (rarely), some host ports may cut the supply off at 900-1000 mA. Aug 20, 2018 at 16:20

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