Power source

Bluetti EB3A

That's all it is. A regular old power station.

However this one doesn't have a fan running during use and it had the cleanest output among many.
That also means it was the best sounding. Stromtank on the cheap.

It lasts for 2.5 hours of listening in my system.

Balanced output

Instead of 230V and 0V, we now get two mirrored 115V signals. This is part of what improves the sound.

Generally I've found that the ones that sounded the best looked the best referenced to GND. There's a bit of a zero-crossing blip visible here, but some were wildly off. The JNG200 looked quite good, aswell.

Low distortion

Much lower distortion than can be achieved using the mains.

For reference:
Mains distortion is between 3 and 5% depending on the time of day and day of the week.

The Bluetti is between 0.1 and 1% depending on the load.

It took me a while to find the best power station. I tried a couple and here are my thoughts on them:

Ever so slightly more grit than the JNG200, but also no fan spin and better macro dynamics. Overall I find it the best sounding and also the only actually practical one.

Clarity is the best, staging the most precise, etc. It doesn't really show on a graph, but it's really quite good. Bass digs deep, seemingly improved microdynamics, simply improvements across the board. And even when running Hathor at 100dBC which draws like 250 to 300W from the plug I didn't get any fanspin. This is it.

Even so it'll ramp up the fans while charging in silent mode. Technically that could be improved by a software update. I guess I'll have to live with some fan noise when I'm not actively listening to music,

Fantastic sounding, fan is the quietest of the ones that have a fan spinning at these loads, just a little soft sounding.

This is what I'm going to keep for portable measurements, camping, etc. It fits in a backpack, is constructed incredibly well and is quite compact. Obviously not the highest capacity or power rating.

The others I tested I didn't find satisfactory:

Sadly some transformer hum, soft sounding and even some grain.

I had high hopes for this one. The app is the best, it looks the best. A german YouTube channel said it had the best inverter. But it looks like it doesn't.

It's also more efficient both at charging and discharging than the EB3A.

Loud fans, but bearable

Actually sounds decent, but kinda gritty, not the most well defined.

Still, this one is super cheap, but it ofc has no UPS function. Charging takes forever.

Eliminated, both makes the transformer hum in a nasty way and has unnecessary fan spin, output had a visible blip at the zero crossing.

Didn't sound very good, either.

The R600 has a bit of a zero-crossing blip on its resulting Phase to Neutral waveform, which I think is what causes the transformer growl, IIRC. Even so, they generally all do a fine job of producing a good sine wave between phase and neutral.

Eliminated due to annoying high frequency noise, output looked quite good though.

Sounded somewhat limp.

Eliminated due to loud fan noise.

More transformer hum than the good power stations.

Gritty, grainy. Claustrophobic. Good macro dynamics, but nothing the EB3A can't reach. Grey background.

Frankly I did not expect to see such performance for the prices offered here. This has to be a recent development.