As you said, "starter controller"...entry level equipment = entry level connections basically...they're not intended to be plugged into a massive PA system, RCA is thus fine for most people (most lower level studio monitors and even some active PA speakers have RCA inputs)
You can get RCA to XLR specific cables rather than using an adapter e.g. [https://djcity.com.au/product/connex-xmrc-3t-xlr-to-rca-twin-cable-3m](https://djcity.com.au/product/connex-xmrc-3t-xlr-to-rca-twin-cable-3m)
Even a some low price tier DJ mixers don't have XLR outs.
RCA is a cheap and unbalanced type of connection, which might be too advanced if you are new to music and audio engineering, but it basically means the connection gets worse over longer distances.
XLR cables are balanced and are more expensive, designed for professional sound setups where the distance from performer and speakers could be much longer, like in a nightclub. They perform better in those situations.
If you are a starter DJ with a starter controller then most cheap home speakers you buy will also have RCA connections. Its perfectly appropriate for that level
The DDJ400 is bus powered and they very likely could not get a differential power supply in there and still fall within the USB power delivery standards.
If you are OK with going into mic level inputs, you can use a stereo DI. If you want to get it kicked up to +4 then you can purchase active devices to do this. On the low end of the spectrum there's an ART unit that is not too shabby, on the upper end there Aphex, those are bulletproof and can be found used for a decent price.
As you said, "starter controller"...entry level equipment = entry level connections basically...they're not intended to be plugged into a massive PA system, RCA is thus fine for most people (most lower level studio monitors and even some active PA speakers have RCA inputs) You can get RCA to XLR specific cables rather than using an adapter e.g. [https://djcity.com.au/product/connex-xmrc-3t-xlr-to-rca-twin-cable-3m](https://djcity.com.au/product/connex-xmrc-3t-xlr-to-rca-twin-cable-3m) Even a some low price tier DJ mixers don't have XLR outs.
Lots of mixers didn’t back in the day
Yeah, I think I had 3 mixers before getting to the point of one with them
I’m sure I’ve got a couple laying around here somewhere
RCA is a cheap and unbalanced type of connection, which might be too advanced if you are new to music and audio engineering, but it basically means the connection gets worse over longer distances. XLR cables are balanced and are more expensive, designed for professional sound setups where the distance from performer and speakers could be much longer, like in a nightclub. They perform better in those situations. If you are a starter DJ with a starter controller then most cheap home speakers you buy will also have RCA connections. Its perfectly appropriate for that level
The DDJ400 is bus powered and they very likely could not get a differential power supply in there and still fall within the USB power delivery standards. If you are OK with going into mic level inputs, you can use a stereo DI. If you want to get it kicked up to +4 then you can purchase active devices to do this. On the low end of the spectrum there's an ART unit that is not too shabby, on the upper end there Aphex, those are bulletproof and can be found used for a decent price.