The difference is as follow:
1. The general circuit of an AC-DC PSU is the same. a 24V is pretty much the same as 12V. You do lose about 1% on efficiency, and perhaps require bigger heatsinks due to higher current cause more heat, but overall they're the same. If it takes $50 to produce a 400W AC-DC, then it would be the same for a 19V one, or a 12V.
2. The big difference lies in deriving the main 12V rail that your PC uses. In order to do this, you need a complex VRM circuit. This means more LCs, more mosfets, more ICs, bigger boards.
3. Using a 12V straight from the AC-DC means you don't have to do anything for the 12V rail. You just need to turn it on/off through a simple mosfet design. This means fewer components, fewer traces, smaller boards. ETC. The large components that you see on the Dynamo 360, are not even be necessary provided the AC-DC PSU is a good quality unit, if were 12V.
the following two products serve the general same purpose. One is a 12V unit, one is a 19V. Notice how the 12V is half the length.
The above 12V board purpose is to clean up out-spec AC-DC units, so people can be more creative with the power supply they use, while delivering reliable clean power. Of course, it's still a prototype.
If it were to be just a "control" board, you'd see may be a couple capacitors, but no large components and the board will be 80% taken up by connectors.
The reason that HDPLEX is well known in this community, is a lot through KMPKT efforts. He collabs with HDPLEX to help guide their products to benefit the sff community in general. HDPLEX has a built up supply chain and brand name. They can easily design and produce boards and have built up a very reliable reputation doing so.
The 12V PicoPSU is not as... noble. Most of the issue is due to a singular patent by Mini-BOX, that is, a single board attached to a 24 pin ATX. While they enjoy this patent, they do not care to cater to our community. I have to reached out to them, and asked them for collab/custom design, but they said they want a 5000 MOQ. I don't think we even have that many active members.
Because of their patents, there have been a lack of cohesion in the 12V camp. Recently, after a year of frustration, I hope to come out with competing products that are pure 12V. Simpler, straight forward, reliable. I don't think I can quite hit the same price point as HDPLEX, due to their established supply chain and customers, but I can at least provide a very SFF orientated designs for the community. If I had their supply chain, the HDPLEX 160 can be produced cheaper, or more margins for more R&D. And to be honest, I think HDPLEX charges very reason prices for such premium/niche products.
And yes, there will be a 250W Plugin DC board to compete with HDPLEX 160. It'll have to take some workarounds to get pass the patent, but it'll be done. Above 250W, I think having two boards is better.
-thx for reading my long ass post if you made it to the end-