micky wrote:

What USB devices should work through a passive hub?

Low-power USB devices (unless it is the *only* USB device attached to a
hub - but then you don't need a hub for a single USB device).

My old laptop had 3 USB ports but I needed at least 4. I assumed that
it was better to copy files to a flashdrive without putting a hub in the
middle.

Flash drives usually take little power.

Same for my USB speakers.

But those are *powered* USB speakers. They have their own separate A/C
power adapter - unless you got some real cheapies that only get their
power from the USB port. The USB power is only going to supply 0.5A X
5V = 2.5W of power for a USB 2 port or 0.9A x 5V = 4.5W for a USB3 port
(which apparently you don't have); however, speakers are never 100%
efficient. That's pretty limp for external speakers - unless you're
"speakers" are actually a USB headset.

OTOH, my mouse and keyboard xmit so little that I figured they would
work fine through a passive hub. And they did. Total of 4 devices**,
two going through the hub.

Yep, those are low-power USB devices.

The new-old laptop has only 2 usb ports***. Plus I'm probably getting a
3G or maybe even 3G/4G/hotspot USB dongle.

Its specifications should tell you how much power it consumes.

One less port, one more device, so something will have to give. I will
have to put two more things in the hub. In fact I guess I need a hub
with 5 or 6 ports, not just 4. Which of these, flashdrive, speakers,
3G dongle, plus sometimes I copy photos from the camera or the phone)
will work just fine through a passive hub?

So get a *powered* USB hub. Just like powered external speakers, a
powered USB hub gets its power from its A/C adapter, not from the USB
port into which it is plugged.

Just remember that *all* of the USB devices on the same hub will have to
share the parent USB port's bandwidth. Something like a USB network
dongle or a USB printer can generate a lot of traffic which means
conflict with any other USB devices on the same hub.