KenK wrote:

Since the problem USB keyboard I'm using works I guess that indicates
separate fuses. Since I intend to buy USB keyboards in the future I
rashly asume that will not be a problem.

A USB keyboard is not normally a heavy electrical load.

It should fit into a 100mA power envelop (USB2 devices
have classes, and the low power ones, like mice, are
generally under 100mA). The actual keyboard scanning
function, doesn't really need that much power.

There are a few USB2 devices that were high power,
like a certain ADSL USB2 modem that drew 530mA...
from a 500mA circuit :-)

The fuse is not supposed to be "set" anywhere
near the 500mA value, and the fuse is meant to
prevent damage to the pins. So a value of fuse
in the 1 amp range or a bit higher is OK.

Some laptops use "power bug" chips, an
electronic fuse that uses a MOSFET to cut off
power, and some of those work "precisely" at
500mA, to the annoyance of the user sitting
at the laptop. And that's one reason Intel provided
that application note about how to design USB
interfaces, so people would not lose sight of
the intended purpose of cutting off the power.
Laptops don't use Polyfuses, due to the lack
of ventilation inside the machine, and the electronic
fuse (even if it costs a bit more), is a much
more precise device with fewer drawbacks. All
except for "enforcing" the wrong value :-)

Paul