This is a review and detailed measurements of the "travagans tài píng tiān guó DC Filter." It is from a company in Taiwan and the only mention of it is in a couple of facebook posts. A member kindly sent it to me for review. I have no idea how much it costs.The Travagans filter comes in a poorly made Baltic Birch plywood:Oddly, there is a voltmeter inside it which shines through the top if you squint enough:It shows the voltage to two decimal places. I am sure there are people at Apple who are having a heart attack that someone has mastered industrial design and usability better than them!Anyway, the idea of these devices is that they filter the power and hence, the same improvement occurs in your audio. No such proof is of course presented. So let's dig in to see if we can find it.I don't know about you but I don't listen to DC power. I listen to the output of my audio gear instead. So the only test that matters is what happens to the output of an audio product, not what goes in. To that end, I tested this filter using Topping D50s DAC being powered by my computer through its USB port. Everyone knows USB power is "bad" so a device like this has the best chance of doing good here.First, the Topping D50s with straight USB power:And now with the filter at hand:Nothing has changed.Zooming in with wideband high resolution FFT we get the same news:Examining just the noise floor gives us no hope either:Let's pretend with listen to power supply output direct and measure my USB port noise with and without this device:Ah, what do we have here? Yes, noise floor is reduced substantially but what the heck are those nice new peaks? Answer: likely some timer event in the voltmeter inside the device. the killer is that our hearing is most sensitive in 2 to 4 kHz and thing thing is injecting spikes in that very same range!Thankfully our DAC didn't care and filtered this out just the same as USB power. But, the sin is there: this device worsens audibility, not better it.Not only will this device take money out of your pocket, but will also make your desk look ugly too. Please stay away folks. As a minimum, ask for the type of measurements I am showing. Half the time I find these tweaks do more damage than good because whoever built them doesn't even measure them to see if they do what they think it does.------------As always, questions, comments, recommendations, etc. are welcome.They are forecasting subfreezing weather next week and the panthers are asking for warm clothing. Surely you don't want to disappoint them and have them shivering, right? So pleaseusing