One more question..
How would you determine voltage rating of the capacitor if it's not
written
on the cap?

What is the supply voltage in the circuit? Could the capacitor be 10
volts?

A 10 uF capacitor with no voltage marked is unusual.

Voltage rating of a capacitor does not affect the properties of the circuit
unless it is undervolted. You can always use a higher voltage rating than in
the original circuit for capacitors.

The printing sometimes wears off of components and it is no longer visible,
or it may not have been on their if some other marking from the manufacturer
identifies the capacitor.

I would wander around www.digikey.com (download the capacitor section of
their parts catalog) and look at the different sizes, types, and
manufacturer ids.