I bought the linked a/c→d/c PSU 2nd hand. I did not look at the connector (assumed it was barrel) and just focused on power attributes. Then when I got home I noticed it has 4-pins. Luckily there is a diagram on the sticker, which says:
P1,2=+12v
P3,4=gnd
So I imagine P1 and P3 could supply 12v to a 12v device, and same for P2 with P4. Correct? I’m a bit surprised pins 3 and 4 are labeled ground and not negative. It’s a round connector, so I wonder if the outer ring is actually made to be negative. The a/c input is 3 pin (i.e. grounded).
I wonder if I am misunderstanding because I don’t get the point in 4 pins in this context. If the original appliance (LCD or whatever it is) needs two 12V supplies, why wouldn’t it simply be a 2 conductor barrel considering the appliance could internally wire two circuits in parallel?
I bought it to drive a device that needs a barrel. I’m not really happy to cut the connector off b/c I might one day end up with a 4-pin device, but I guess it’s not worthwhile to try to track down a 4-pin female tip locally to rig it up non-destructively.
To be clear, the appliance needs 12v 5A, which is how the 4-pin PSU is labeled. I hope it’s not a case where each of the 14v pins have 2.5A max.
Generally, assume the lower result unless explicitly stated otherwise. If there are two pins supplying 12vdc but only a single output rating, then the assumption should be that the PSU produces a single 12vdc rail, and the total of both pins is 5A max. It is implied (unless otherwise stated) that the full rating of 5A can be drawn from just a single pin.
From a marketing perspective, if there were multiple output rails, they have an incentive for them to list them out in detail. ATX PSUs for PCs do this.
From a safety perspective, it would be downright irresponsible to design a connector on a finished product (like this standalone PSU) that has a lower per-pin rating that what the supply can offer, so any decent pre-built PSU will not have per-pin limits that are lower than the total output limit of that group of pins. As a counterexample, ATX PSUs are a component in a larger product (a computer) and so individual pin limits must be adhered to.