Quick answer: A USB-A port supplies 500 mA to a configured device and up to 900 mA on USB 3.x, and a bus-powered hub has to divide that budget between every port on it. One 2.5 inch hard disk drawing 1 A at spin-up can therefore reset the hub and disconnect everything attached. A powered hub with its own 5 V supply gives each port a guaranteed current, usually 1.5 A or more, and keeps the host port free for data. Buy powered when any device has a motor, a radio or a battery.
The word powered appears on almost every hub box, and it means two different things: a hub that takes a small DC input, and a hub that simply passes the host current through. The first solves problems; the second is a passive splitter with a plastic shell. The difference shows up the moment a device needs more current than the port can spare.
What a host port will actually give
The current budget
USB 2.0 defines 100 mA for an unconfigured device, 500 mA once configured, and up to 1.5 A on a dedicated charging port that may not enumerate data. USB 3.x raises the configured figure to 900 mA. A laptop port often caps lower than the specification when running on battery, which is why a device that works on mains power fails on battery.
Why hubs make it worse
A bus-powered hub is itself a device drawing from the host, and it must share the remainder. Four ports on a 900 mA budget is 225 mA each before the hub’s own consumption, which is not enough for a keyboard backlight, let alone a disk. Overcurrent protection then trips, and the operating system reports a surge or simply drops every device on that hub.
What “powered” should mean
A real supply, not a pass-through
A proper powered hub has a 5 V supply rated for the sum of its ports, typically 2 to 4 A, and often a 12 V input with internal regulation for stability. Check the supply’s current rating against the port count: four ports at 1.5 A needs 6 A, and most bundled supplies are 2 A, which is why the specification usually promises 900 mA per port rather than 1.5 A.
Backfeed and the host
Some powered hubs feed 5 V back into the host through the upstream cable. That is convenient for charging a laptop only if the hub and cable support it, and it is a fault if the host does not expect it. A hub that backfeeds into a port not designed for power delivery can keep a machine from shutting down or, in the worst case, stress the port protection.
Power per port, compared
| Hub type | Supply | Per port | Handles |
|---|
| Bus-powered, 4 port | Host only | About 200 mA | Keyboard, mouse, dongle |
| Powered, 2 A supply | 5 V, 2 A | 900 mA | SSD, card reader |
| Powered, 4 A supply | 5 V, 4 A | 1.5 A | 2.5 inch HDD, phone charging |
| Powered with PD passthrough | 100 W input | 1.5 A plus 85 W to host | Laptop plus peripherals |
Choosing one for a desk
Count the devices that have a motor or a radio: external drives, optical drives, USB audio interfaces with phantom power, Wi-Fi adapters, phones charging. Each of those needs a guaranteed current, and they should not share a hub with a keyboard that reports a fault every time the disk spins up. Keep high-current devices on the powered hub and low-current ones on the monitor’s ports.
Check the upstream cable too. A hub is only as fast as the lead that connects it, and a charge-only lead caps the whole hub at 480 Mbit/s. The USB hubs overview covers port combinations, the Type-C hubs page covers the C-host equivalent, and the USB hubs with USB-C guide covers models that accept power while feeding a laptop.
Practical scenarios
- Two external drives on a laptop: use one powered hub with a 4 A supply rather than two bus-powered splitters, and keep both drives on the hub so they share a stable rail.
- Conference room table: a powered hub keeps a guest laptop charging while it drives a display adapter, provided the hub passes at least 60 W and the display is on its own port.
- USB audio interface with phantom power: phantom power draws a burst at switch-on, so give the interface its own port on a powered hub rather than sharing with a drive.
- Wall-mounted TV stick: use the manufacturer’s supply, not the TV’s service port; a stick that browns out reboots and loses its network settings.
FAQ
Does a powered hub charge devices faster?
It can, because the port is no longer limited by the host budget. A 1.5 A port charges a phone faster than a 500 mA laptop port, but it cannot exceed what the charger inside the device requests. For fast charging above 15 W, the device needs USB Power Delivery, which a USB-A hub cannot provide.
Why do my devices disconnect when the drive spins up?
The hub is hitting its current limit and the port protection is cycling. A 2.5 inch drive can draw over 1 A for a second at spin-up, which exceeds an unpowered hub’s share. Move the drive to a powered hub or directly to the host, and check the supply rating before adding another device.
Can I use a phone charger as the hub supply?
Only if the voltage matches and the current is sufficient. A 5 V 2 A charger will run a four-port hub at reduced per-port current; a 9 V or 12 V charger will not work on a 5 V input and may damage the hub. Use the supply that came with it or one with identical voltage and at least the same current.
