The DC-powered OpenSprinkler is designed to work with 24VAC sprinkler valves as well. The way it works is to simulate the behavior of solenoid valves under AC. Specifically it generates a relatively high impulse voltage to engage the valve, then lowers it to input voltage to provide holding current.
From your picture it looks like you also use wired Ethernet module? I think the problem is that under 12VDC input voltage, there is quite a bit of power dissipation — the DC controller uses a linear regulator to drop the input voltage to 5VDC. With wired Ethernet module, the current consumption is quite high (about 250mA), so this produces a power dissipation of (12-5)*0.25 = 1.75 Watt power dissipation, which probably burned out the linear regulator. The DC-powered controller usually should work with a low-voltage input adapter, the ones we include here for the US market is 7.5VDC. So while it can accept 12VDC, the problem is that 12VDC plus the wired Ethernet module becomes a problem. I apologize for the issue because we didn’t anticipate this usage situation when designing the controller.
So the short term solution is to use a lower-voltage adapter, like 7.5VDC or 9VDC. We will be redesigning the DC driver board to use a switching regulator which would work much more efficiently with high input voltage.