You take them apart, and see if they're any good :-P
Luckily, they're cheap as dirt (I bought 9 pretty green braided flat micro USB cables for $7.50 this week - though I haven't chopped any) so it's not going to break the bank. You can also, for only a small premium, get cables that just end in the 4 wires, or in a barrel jack (ebay) - like 1.50-2.50 a pop.
I would prefer generic cables over fancy brand name ones for chopping up (and in general - I'm cheap). The branded ones are more likely to do something weird (like your apple ones did).
As it happens, I have a bunch of USB A male to USB A male cables. Like, over 100 of the damned things - I can't think of any use other than chopping them up to get USB power cables for projects (you get 2 for 1). I need to sell them or something...