Minor point but when I went and looked the shell was $35 and the modules were $36. Still, 2 shells, 2 modules - @$35/$30 that's $130, plus cables. Its a lotta money.
Actually I take that back. Went back and looked again and that is a dual module already @$35 on sale (reg $40, also out of stock atm) so you only need one shell. So that makes it about $100 plus cables for your dual setup. $35 for the shell, $36x2 for the power modules, that's $107 plus whatever the cables cost.
TL;DR - Your setup will support up to 8 UDs, not just 2.
The power supply is limited by the current draw of the devices you plug into it, not the required voltage. Given your VVPS will go up to at least 12, and given that UDs are a 1a load, what you need is a device capable of putting out 2a or 3a to give you some head room (hence I would look for 3a to run 2 devices without ever maxing it out).
Those modules go up to 5a - that is plenty to run 4 devices and still not max it out. With ONE module, and one shell. And a splitter cable. You can get a 4 way splitter (I only need a 2 way splitter).
Think of the voltage as if it is a water tank (this is not really all that apropos but I think its a good enough analogy for now). Then the cables are water pipes. The water is current. The device you plug in is a pump. The pump pulls the water (the device pulls current) up to the max it can use, which for our purposes is 1a for the heaters in Underdog log vapes.
The power supply in your case can provide 5a per module.
So the pumps (our UDs) will only pull 1a of current max NO MATTER how much amperage is available. (No matter how full the tank is, the pumps only pump at 1g per minute so that's all the water that will be pulled through the pipes). We're going to assume that the tank refills exactly in pace with the outflow - like I said, not a perfect analogy, since voltage doesn't really get "used up" like water would (ignoring little details like voltage drop due to resistance which is basically how the heaters work, heat is created by the current running through the wires).
Now if you plug SIX UDs into a 5a power source, nobody will get their full 1a of current because there is only 5a available and you are trying to pull 6a.
Obviously there is a lot of stuff involving resistance, atoms, electrons, and a lot of other details of electrical engineering but basically that's what you need to know for these purposes. Get a VVPS that provides one more amp than you need to run your device(s) so you never max out the power supply (which would shorten its life and also NOT provide you with the full 1a that you need in a stable reliable fashion - it's likely to drop out from time to time at the edges of what it can provide and what you are trying to draw from it).
When you adjust the voltage you are changing the current delivered - if the voltage is reduced, less current will flow and will create less heat in the resistance heater inside the UD. If you increase voltage it (should) increase current flow. With our plumbing analogy, changing the voltage setting is like changing the water faucet - open for more water flow, close it down for less.
So your VVPS needs to go up to 12v, but as long as it can provide the amperage for each device, that's all you need no matter how many devices you plug in. 1 device, 12v max. 2 devices, 12v max. 100 devices - 12v max assuming your power supply is capable of delivering 101 amps (plus one to avoid hitting the max although if this 100a power supply was for real you'd probably need more than 1 extra amp depending on how much fluctuation there is per device on average).
So you don't really need a double power supply to run two devices. You just need something that hits your voltage target (usually 10-12 a for most people with UDs) and can provide enough current for each device (1amp per UD log vape). With this setup and leaving headroom to not stress the power supply, you can run FOUR devices per bay, or a total of 8 UDs. (Oh yeah and the appropriate splitter cables).
Could be useful in a party situation?
