After you have flashed Sonoff Zigbee 3.0 USB Dongle Plus or any CC2530/CC2531 USB adapter(s) with Zigbee Router firmware then you only want to use a standard USB charger as a power supply for it and not have it connected to a computer (as it will no longer use the USB to communicate), and you want to place it far away from any other electronic devices/appliances which can cause EMF/EMI interference.