I love how the 3.5 mm connector is now called aux

The Apple dongle is very good and very cheap. YMMV on Android - it should be fine but I recall seeing some complaints a while back. Don’t remember what the issue was.

You can see its DAC measurements here: https://www.audiosciencereview.com/forum/index.php?threads/review-apple-vs-google-usb-c-headphone-adapters.5541/

It’s often recommended as an entry-level DAC for audiophiles who want to focus their budget on amps and speakers when starting out. It’s transparent and there’s no need for any reasonable human to ever replace it, as far as sound quality goes. Build quality and connections are its limitations.

My PC has an Aorus Master x570 MOBO with “high end” (above average) onboard sound, and the $9 plug-and-play Apple dongle was a noticeable improvement. Almost every external DAC will beat onboard PC sound, but this thing is silly. It’s worth a try - return it if there’s any compatibility issue, or keep it handy for other uses, but I imagine any bugs are resolved at this point.

The audio quality of a USB to headphone jack can vary wildly as they need to contain their own DAC (digital->analoge converter), tbh most are probably good enough for most people but depending on your headphone setup you may be able to tell. (Depending how much you spend they can actually have better audio quality than a normal phones headphone jack)

Edit: Fiio makes a pretty nice one, but not the cheapest on the block

It depends on the dongle and the DAC inside.
For example, the Meizu HiFi Pro dongle I use sounds better than the headphone jack in my Pixel 4a.

I do know the Apple c-3.5 is the best value. It sounds balanced, has little distortion, and puts out decent power.

If you want the end-all-be-all, the Nexdrive Spectra has a very similar audio chain to the popular Quad Amp LG phones.

The USB C to 3.5mm dongles out there are plentiful and to be honest you can't really go wrong with any one. At the end of the day, they all behave pretty similarly as they contain a DAC and an amp built them. At this point, the world of audio has gone far enough that decent audio chips are pretty cheap and it's not all that likely you'll actually hear any significant differences between different dongles.

If you are an Android user, be wary of which dongle you get if you're looking at the Apple ones. Depending on the region the dongle is made for, some users report issues where the dongle chooses not to amplify the signal properly. I ran into this problem with the model MU7E2AM/A and it's just annoying. Android and external DACs can be kinda hit or miss for some reason, and the dongle only functioned properly using a specific music player app that kinda overrides the system and forces it to use the DAC (the app is USB Audio Player Pro).

You can buy dongles pretty cheap on the cheapo sites like Aliexpress, which isn't a terrible idea. You could buy a few cheaper ones and be fine for a long while. I've had issues with the longevity of certain dongles, daily use can sometimes put physical stress on the USB connector if you're not careful, which is why I would just keep a few different dongles and chew through em as needed.

Apples USB-C DAC dongle is available locally, cheap including shipping and basically best at price point (cheap) unless you want to roll the dice with Alibaba or similar. I have 3 because dongles tend to disappear, with them being tiny and all. I had others from international sellers but they all disappointed except for audio volume.

I bought a ugreen one from Amazon that had a y-split so it could charge and play aux out at the same time.
It had a crackle ☹️ (regardless of if it was charging)

But my cheap nobrand straight USBC to aux from Amazon I bought ages ago has been great.

I think it's a toss up unless you're going with a name brand converter (apple as another said, agree there - price vs performance will always be good) or a more powerful DAC like a Fiio.

1. Definitely get some IEMs. They're awesome. I have Westone Audio Mach3s and I love them.

2. I have a Pixel 8 so no 3.5mm so had to get the dongle.

3. Dongle is good. It lives at the end of the IEMs cord. I read USBC transfers data better than 3.5mm? That plus built in DAC and high res /flac audio = an excellent listening experience.

I’m sure you are aware of this, but the same company makes a phone intended for music also.

https://moondroplab.com/en/products/miad01

The USB-C version of the Moondrop Chu 2 comes with a DSP cable, which basically is a digital tuning refinement on top of the IEM's base tuning, and I believe you can change profiles on those using an app. You can simply just get that and also a regular replacement 3.5mm cable, if you'd like.

Depends on you and the phone.

My old lg v60 has a headphone port and sounds better than almost anything.

My last gfold 3 sounded ok with a cheap dongle but great with a rhodium off Amazon. Cheap dongle was fine too.

My current pixel fold sounds marginal with a cheap dongle but great with the rhodium.

Depends on your ears, have Shure 825s or whatever and Etymotic er4xrs for more casual stuff, the rhodium and v60 are incredible, fold can push them, the pixel again clearly isn't tuned as well.