Ideally, it should be the point of them, Bonny. Unfortunately, pass
through designers didn't bother to fully check the USB specification when they started designing "USB-compatible"
devices, IMO. The only part they really complied with is the connector and the voltage spec of 5V.
According to the USB specification, PC USB ports are only required to provide 500mA. Some will provide more in order to work with higher-power USB peripherals, so if yours does, you're lucky. But it's largely hit and miss.
External USB
devices like powered hubs and AC-USB adapters generally provide more current, but not always. Further, some will be rated for a higher total current for all ports, but are still only rated for 500mA per port. Your best bet is to always check the spec of the port you're using, and never exceed what it's rated for.