Hello the BTA 30 Pro can be easily powered with an Apple USB power dongle.
A USB-A to USB-C cable is included with the device.

It only needs power if you only use it to receive Bluetooth devices, which are then output via Coax, Toslink or RCA jacks,
It also needs power if you want to listen to a source via Bluetooth with headphones via coax or toslink.

If the BTA 30 Pro is connected via PC or laptop, it takes power from these devices.

I recommend this power supply for an absolute power supply:

iFi Audio iPower MK2, Ultra Low Noise power supply (approx. 75 Fr. at K55).
It can be used universally for many devices. Just buy the 5 volt version.

The Apple power adapters with USB-C connection are also very good,
where you feed the BTA 30 Pro with power using a USB-C to USB-C cable.

Question

Hello the BTA 30 Pro can be easily powered with an Apple USB power dongle. 
A USB-A to USB-C cable is included with the device.

It only needs power if you only use it to receive Bluetooth devices, which are then output via Coax, Toslink or RCA jacks, 
It also needs power if you want to listen to a source via Bluetooth with headphones via coax or toslink.

If the BTA 30 Pro is connected via PC or laptop, it takes power from these devices.

I recommend this power supply for an absolute power supply:

iFi Audio iPower MK2, Ultra Low Noise power supply (approx. 75 Fr. at K55).
It can be used universally for many devices. Just buy the 5 volt version.

The Apple power adapters with USB-C connection are also very good, 
where you feed the BTA 30 Pro with power using a USB-C to USB-C cable.

Answer

In the meantime, I have found out for myself what is needed. A 5V power supply with 500mA is sufficient to operate the fiio bta 30 or the pro version. A 5V power supply with 1A also works, of course, as the device only needs 500mA.

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Question about FiiO BTA30 Pro