I have personally had success in plugging two low current devices in to a Socket Power Pack. I used a USB- 3 Outlet Splitter. Everything worked fine until I plugged in something with a higher current draw, then the splitter turned off and acted like it had been unplugged. Once I unplugged it and then plugged it back in, the two low draw devices worked fine. I think the limitation is mainly in the type of USB splitter that you use.

The two devices that I had were the NANO and the Collibri II. They worked fine together. Once I plugged in my phone (XC SOAR) it had issues and nothing got external power.