It's probably a problem with my devices. I've never seen these problems with more expensive devices, but my cheap bluetooth speakers will only charge with certain cables.

I also have cheap cables that don't seem able to do data transfer. Guessing it's not actually following the USB-C spec.

Are your bluetooth speakers connected over a C-to-C cable or is there any legacy USB in the mix (type-A and/or microusb)? The reason I ask is legacy USB expected 5 volts to be supplied by default, whereas in type-C you have to specifically request any current. So some C-to-A / A-to-C adapters/cables include the resistors to request the current whereas others do not, leading to legacy USB devices not getting power through some adapters/cables.