I have an old Nokia phone which charges fine from the adaptor, but refuses to charge using a USB charging cable.
Note that this isn't a normal USB cable, as you can see from the picture, it's got a USB A connector at one end, and a Nokia DC jack at the other.
What's strange is that even if connect this cable to a beefy 5v power supply, the phone still refuses to charge. I know that power is getting through because I can measure the voltage at the phone end of the cable, and the phone seems to notice when I connect the cable, but still won't charge.
Do Nokia phones have some nasty trick they use to prevent unlicensed chargers working with them?
Answer
The old Nokia phones using a 2mm charging connector will refuse to charge if the supply is not current limited. I can't point you to any reference/datasheet but from my experience in building a home-brewed charger, you need to limit the supply to deliver around 100mA. I don't have my schematics handy right now but the circuit I used was based from LM317.
EDIT:
Here's the schematic for the charger I built (page 22 of the LM317 datasheet): 
I replaced the 1ohm resistor with a 0.82ohms 5W resistor to get around 300mA of current (which falls within the limits in the Nokia datasheet). Also instead of 1.1Kohm, I used a 5Kohm trimmer so I can adjust the output voltage to 5.5V. Supply voltage is 12V so make sure to mount the LM317 on a decent heatsink. I have over-sized capacitors for input and output as I only have 2,200uF 25V available at that time.
Here's a photo of the kludge charger: 
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