Yeah a higher voltage or higher current capacity power source could be compensated with a simple resistor.
This isn't a great way to charge NiCds though. Normal charge procedure would be at least 10x that current, and then stop the charge when the peak charge is detected. Charge detection is a trick- the battery voltage actually drops, but not very far and not for very long. Or stop the charge when the battery begins to warm up (indicating the power being delivered is turning into heat rather than storing as chemical energy).
Trickle chargers like this are slow to charge the battery, and never stop slowly overcharging when full, which reduces the overall life of the battery. But it's still quite common.