Tablet discharging into and charging dac/amp

[Asylum Seeker]

Folks, my two Android Pie devices (Samsung Tab S4 and Huawei Mate 20X) discharge into or charge the portable DAC/amp (Oppo HA-2) when connected. I've tried chaining the USB connection settings in Developed Options, but there's no change. The cable is USB C to micro USB. Any way to prevent this? Is it a cable issue?

 

[0bs3rv3r]

On my Fiio DAC/amp there is a switch to stop this happening, but it is an older microUSB type. I thought USB-C would be smart enough to know whether to draw charging power or not. Therefore it might be a cable issue preventing this working.

 

[Asylum Seeker]

Yes, I am thinking it is a cable issue. The Oppo HA-2 has no switch to prevent it from accepting power.