phone charger/usb are the all equal

[Guest GuyAustin]

I have got a spv c550

it came with a mains charger and a pc-usb cable that also charges the phone

I have got a holux slim 236 bluetooth gps device that came with a cigar lighter charger that does not seem to charge the phone even thought the plug fits the phone.

I have got a couple of other mini usb cables that came with various digital cameras etc

Are all mini usb cables created equal.

I just assumed that they would all have 5volts in them on a standard pin

regards Guy