It might be a rare occurrence but one problem I have had with a different system in the past is the failure of the controller's power supply (more than once) which ultimately resulted in the complete loss of my tank, so it is a bit of a concern for me.
If I bought 2 Hydros control units, that each come with a power supply, and I connected them together with a power supply in each controller then I would damage the system. If this wasn't possible then, in my opinion, there should be a warning to that effect in that set of instructions. However, it is actually easily possible to use 2 power supplies for redundancy; you just need to use a different command bus cable so that the power doesn't transfer between the 2 controllers.
I'm entirely new to controllers and am reading back through these old threads regarding Hydros as that is what I've bought for my new (undelivered as yet) tank. I'm about half way through that monster "Hydros Owners: how happy are you long term?" thread
Am I reading it correctly that you are saying using two controllers and connecting with their command bus cable (power + data) and if both have their own power supply then it will damage the controllers? I hadn't seen that listed anywhere. Maybe that is what you are saying by saying there should be a warning? Or was your statement "If I bought 2 Hydros control units, that each come with a power supply, and I connected them together with a power supply in each controller then I would damage the system" meant to be a question?
I currently have the setup as XP8 (powered) connected to X4 connected to WEv2 (powered) connected to XS. All using the powered command bus cables. If I set up a water station in the garage I'd probably run a long data only cable out to the one out there.
Thanks for any clarification.