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?
My understanding is you can use any lightening to USB cable, but I’ve only used a camera adapter so not sure if they all work or provide sufficient data transfer rates.  I have also heard the Apple Camera Adapter with the power port sounds a bit better but I haven’t confirmed this.  They’re not all that different in price so unless size is a factor I’d just buy the powered version.  I did buy a cheaper 3rd party cable with the power port and I found it sonically inferior to the base Apple CA without power port.  I haven’t looked but I have to believe there are higher-end lightening-to-USB adapters that sound better than either Apple cable, and that’s the direction I’m going next and will report back with any findings. 

As as far as your side question, I have no idea.  I know my AQ Dragonfly Red sounds better than the iphone’s or ipad’s DAC as one would expect.  My priority is sound quality, so I don’t buy Apple ‘phones of any kind and never looked into what DAC they use or where.  Hope this helps. 
Thank you for reply.

My question is “do I have to use Camera Adapter when I can directly connect iPhone to DAC by Lightning-USB A/B?”

From my basic understanding, less device, shorter case should sound better. So, using camera adapter (more device), so making the total sound travel distance longer(longer) seem counter-intuitive.

I thought that one of followings might be the reason.

1) due to certain Apple’s certain technical restriction, I can’t simply use a cable alone to bypass apple device’s internal DAC


2) Camera Adapter has some sort of sound enhancing device.(?)

Have you tried connecting Apple device to external DAC without using Camera adapter?

In case of Dragonfly type DAC (Audioquest) I can see why I need a camera adapter simply to avoid error message. But in case of other self-powered external DAC, I do not understand why I need to go through camera adapter kind of external accesory.

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.