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.
In this photo it’s simply saying if you need 12v on the right dont use this power supply because it’ll go into the 5v side of whatever you’re powering. Keep in mind these are just standard din connectors. They’re not tied to a standard pinout and are used for all kinds of things
WRT your op it’s about current capacity of the connector. If I have a device that needs 12v at 8 amps but each pin is rated for max 5a I can deliver 12v at 4-5 amps through two pins and tie them both to the power rail on the pcb to get a full 8a capacity
That’s interesting and perhaps it explains why there would be two 12v pins (so they can be combined to give double the current). But the question remains as to whether “5A max” on the label implies 5A max per pin, or 5A max total when combined.
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.
5A max is certainly for the adapter, not the pins. Pins are an implementation detail, that sticker is telling you what the supply is capable of.
Also, check the power rating. 60W, 12V means a max 5A output.