Powered vs Bus-Powered USB Hub: Which Do You Need?
Summary
Choose a powered USB hub when your connected devices need more power than the computer's USB port can supply. A bus-powered hub draws from that port; a self-powered hub uses an external adapter. Compare the total device load with the hub's limits, and treat USB-C charging for the laptop as a separate specification.
Compare the two power sources
| Question | Bus-powered hub | Self-powered hub |
|---|---|---|
| Where does its power come from? | The computer's USB port | An external power supply |
| What limits the connected devices? | The host port's allowance, shared with the hub and devices | The hub's total and per-port output limits |
| What should you verify before buying? | Whether the host port can supply the combined device load | The included or required adapter and the output available to each device |
| Does it charge the laptop? | Do not assume it does; check a separate USB-C PD specification | An external adapter alone does not establish laptop charging support |
Bus-powered and self-powered
Plugable, a hub maker, defines the two plainly. A self-powered device "takes all of its power from an external power supply," and a bus-powered device "takes all of its power from the host computer's USB interface."
Some hubs do both. Plugable notes that "Many devices that include power adapters, especially USB hubs, will function in either self-powered or bus-powered mode," and adds that if a device comes with an adapter, "it should stay connected at all times, otherwise the device may not function as designed."
How much one port gives
The numbers are small. According to Plugable, the USB 2.0 specification "limited the power that could be drawn from any USB port to 500mA," and USB 3.0 raised that to 900mA. Some USB-C ports give more, at what Plugable calls the commonly found values of 1.5A or 3A at 5V, or 7.5W and 15W. Microsoft's USB-C FAQ uses the same top figure: "up to 5V, 3A, 15W."
A bus-powered hub splits that one allowance among everything plugged into it. On a USB 3.0 port with 900mA available, two devices that each want close to the full 900mA are asking for 1.8A from a port that gives half that. The hub itself can add a limit too. Lemorele's TC38L lists device charging on its three USB-A ports as "total 5V/3A, max 1.2A per port," so no single port goes past 1.2A and all three together stay within 3A.
What running short looks like
On Windows, the sign is a notification titled "USB device might need more power," which reads "Your PC might not provide enough power to the USB device. Please connect your device to external power, or try using a different PC." Microsoft's suggested fixes are to plug the device into external power if it can take it, and to "Disconnect any unused USB devices that are connected to your PC."
The worse case is a drive dropping out. Plugable warns that "If the power runs out, any USB device attached to the computer may suddenly disconnect, which could result in permanent data loss for a USB storage device." That is the situation a hub with its own adapter is meant for, and Plugable names "USB hubs or external hard drives" among the high-current devices that may need it.
Charging the laptop is a separate job
The port marked PD on a USB-C hub can be doing a different job. On the TC38L, the PD port "Supports fast charging up to 100W; charging only, no data or video transmission," and it exists to pass a charger's power through to the laptop. The page doesn't say whether that charger also feeds the USB-A ports. Our guide to hubs with HDMI and charging covers the laptop side of that. Going the other way, a hub's own USB-C ports may not charge a laptop at all. Plugable says "Not all USB-C ports on devices (like a hub or dock) offer PD charging, some USB-C ports may only offer standard USB 3.0 power at 900mA."
Browsing for one? Browse docks and hubs in the feed →
Sources
- Plugable, Self-Powered vs Bus-Powered USB Devices
- Plugable, USB Device Charging
- Plugable, USB Power Delivery and Charging Battery-Powered Devices
- Microsoft Learn, FAQ: USB Type-C connector on a Windows system
- Microsoft Support, Fix USB-C problems in Windows
- Lemorele, TC38L USB-C 8-in-1 Hub
We have not tested these products. Specs and guidance are as published on these pages on the date above and can change; the manufacturer's page for your model has the current details.