IPhone/IPad - why do I need camera adapter to connect to DAC?

When to connect latest iPhone / iPad (Lightning connection / USB-C connection) to external DAC,
why do I need a camera adapter?
(Unless I want to charge the device while listening)
Can I just use one of following without a camera adapter?

1) Lightning to USB A (if the external DAC has USB A input)
2) Lightning to USB B
3) USB C to USB B

One dealer told me that in case of camera adapter, there is sound quality difference between one with power and one without power.
If I don’t need to charge the device while listening, can I just buy a cable to bypass iPhone’s internal DAC?Or does camera adapter has a spacial function?

Side question: When I connect earphone, I need an adapter. Apple puts dac in here for wire earphone.
Does apple use the same dac in its airpod pro / wireless earphone / headphone?
If your DAC supports Apple AirPlay2 (like my Matrix Mini-i-3 Pro) use that wirelessly. I was surprised how well that works. I think the wireless maybe better because the noise of the phone is not directly connected to the DAC. I am not an expert in Apple crap but I am just using AirPlay2 temporarily until my DAC is ROON READY.
I think I will need a streamer. The DAC I happen to like it doesn’t have streaming function.

I like AirPlay2, and since I don’t have any better source than CD, the quality is just fine. 

I’ve been thinking about Roon, but simply doesn’t want to do any sort of subscription yet.
I believe the iPhone/iPad does not have enough electricity as a source. With the camera adapter the charging cable would support enough power to drive the iPhone.

When I connect the iPad to my Oppo 205, I use the Apple AV adaptor. Then use the HDMI cable plus the charging cable to make it work.