Gregory's Server@jplatte @luana @bcoffy the way USB is designed, the host device (indicated by using A connector) is supposed to supply power
if both devices decide to supply power you end up with current fight where both device supply 5V power, and the consequences of that could be pretty bad
this is not a problem with USB-C, as USB-C has a way to negotiate who is responsible for supplying the power
USB-C to USB-A/USB-B adapters are fine provided the user doesn't use those to create a male USB-A to male USB-A cable, however the possibility of someone creating those and then causing damage to their hardware (for instance, a less tech-savvy user could try connecting two computers using usb-a to usb-a cable) means that those adapters are forbidden by the spec
as for your external HDD, i assume the manufacturer wanted to save money using USB-A instead of USB-B, USB-C or custom connector as they should be using
@xfix @luana @bcoffy
Aha! So my male-B-to-female-C is actually fine then because it doesn't make it easier to make A-to-A connections?
Also *how* forbidden is this really? It seems like A-to-A is pretty simple to obtain. (though then again I've seen something about male-to-male US power cords that you can apparently get easy enough and those *got to be* super illegal to manufacture so maybe simple-to-obtain means nothing)