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I've had problems with one long (4 meter) USB Mini-B to USB Type-A cable not being able to boot a 2.5'' external hard disc due to not supplying enough current. On top of that, the cable used a Type-A to Mini-B adapter for the Mini-B part, which probably made things worse.
Three different shorter cables I got around made the hard disk work without extra current, so it was definitively the cable's fault. However, if I plugged the hard disk to the power, and used the long cable just for data it worked.
Here is some related information on powering through USB cables:
I have not any long cables that don't have an intermediary Type-A to Mini-B adapter to try them out.
My question is: is there a way to guess if a cable will provide enough power for charge/disk drive power? Is it related to the length of the cable, to the build quality of the cable, or the fact that uses intermediary adapters?
Updates:
Thanks for the answers guys. The computer is a Macbook Pro 13' (2010), so the USB connector is directly soldered to the motherboard (no front panel USB).
Up so far the most convincing explanations seem the ones from @user12889 (the USB device being over the spec and causing problems because of that) and @Tog (the adapter in the cable causing the power loss), although everybody else provided useful information too.
How do you know that cable is unable to supply current? Does it overheat and are there any traces of melting? – AndrejaKo – 2011-01-10T18:53:28.263
2If the cable needs adapters, then it is not standards compliant. Replace it with a true USB2.0 certified cable, and all will be a lot better. It may not be perfect, however, because the drive itself may be stretching the standard as well. – RBerteig – 2011-01-11T09:15:54.480
AndrejaKo: When I say 'unable to supply current' I mean that the HD won't boot with the long/adapted cable unless I connect the additional HD power supply. With the short/unadapted cables the HD works fine without connecting the additional HD power supply. – Ricardo Sanchez-Saez – 2011-01-12T11:47:59.610