Whats the maximum current I get out of the USB port of the Pi Zero? I'd like to power USB Speakers (5V 3W). Is that possible?
For the Pi2 the current limit is 0.6 A. (Don't know the specs of the Zero, but i think it is also around that level) Thats what your Speaker uses. So it MAY work. I would just try it. What is the worst thing that could happen? Fuse would turn the Pi off, you unplug the speaker, fuse would reset and the Raspberry Pi would reboot.
If it does not work, maybe try
max_usb_current=1 in the
/boot/config.txt. That changes the Maximum USB current to 1.2 A. Then you should have enough power.