My cellphone doesn't charge on a power-only USB cable

I have wireless speakers that charge their batteries from a USB port. They came with short USB cables that carry only power. When I plug my cellphone into this cable it won't charge. I don't mind, but I've read about people getting their phones hacked or eavesdropped when they plug into USB ports in public places, such as airports. I've read recommendations that they use power-only cables to prevent this.