If you're thinking about picking up one of these, I am very happy with the Matrix X-SPDIF 2. I upgraded to it earlier this year after enjoying the original X-SPDIF for quite a while, and it turned out to be an awesome purchase.
It's currently plugged into my Mac via USB and I'm not using an external power supply. I originally bought it so that I could feed more than one DAC simultaneously (via AES, S/PDIF, and TOSLINK), but it proved even more useful when I picked up a DAC with I^2S support.
Note: it seems perfectly happy sending output to all its interfaces at the same time, so this is a great tool if you have multiple DACs that you'd like to A/B test.
The X-SPDIF 2 is now driving my Holo Audio Spring DAC (KTE Level 3) via I^2S using a short (2-foot) HDMI-spec cable. I wasn't sure how easy this would be, or whether I would need to play with the dip switches on the underside of the chassis to make things work. But I was happily surprised -- everything was plug and play. It's now playing anything from 16/44.1 to 24/384K or DSD64, DSD128 and DSD256, fed directly from Audirvana Plus on macOS.
Note: One thing I noticed is that it sometimes doesn't come back after the Mac has been asleep -- so I've found myself unplugging it and plugging it back in if it's in a coma. A minor nit, but otherwise, it's been flawless.
Physically, the X-SPDIF looks great! I like the look a lot better than the Singxer, which seemed awkwardly large and a very big ugly logo on the front. The Matrix has a very subtle design with only a single multi-colored LED light on the front. Green means PCM, and Blue means it's detected DSD content. As people mentioned earlier in this thread, the case is super-solid and well-built. Although it is a little larger than I was expecting -- it's about four inches square. You can get an idea of how big it is in the picture below.
I bought it from Shenzen Audio, and they delivered to California within a few days. It was a tough call to spend almost $400 on an upgraded USB bridge, but I'm actually quite happy with the purchase -- and now that it's driving the Spring DAC over I^2S -- it's phenomenal!
BTW, if anyone is looking for the original X-SPDIF for a good price, let me know -- I'm not going back!