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Andreas15
I know, but is that only for shorts internally in the PSU or also for shorts in the circuit it is powering?

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Andreas15
No, indeed, I was running 2 seperate PSU's, because the Velleman board uses 15V. The other PSU was only running the heated bed.

To me it looks like something around the little potentiometer that adjusts the voltage is wrong. Because I can perfectly hook up a 12V fan to the PSU and it will run, but just slower. It's also no fixed value. I've measured from 7.4V to 8.7V... I'm just not sure, because it worked perfect for more than a year on 12V, just the setting how it came. And now after switching it to the Velleman and increasing the output a little it's dead a day later...

Is a MeanWell protected to shorts in the circuit it powers? Say the heated bed it is powering shorts, will the PSU be dead than, or do the MeanWells have a failsafe for that?

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Andreas15
Al I want to know is if it is because these are cheap chinese PSU's, I've already ordered a new MeanWell by now, but I don't want to fry that one, so I want to be sure it is just the PSU and not something else in the system that is causing this...

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the_digital_dentist
Switching power supplies are power limited. If you turn up the voltage, the maximum current they can supply goes down. DC power = voltage x current. Since power= current^2 x resistance, if you double the voltage (which doubles current) you quadruple the power.

When power supplies fail, they usually shut down completely. Since the voltage reads low you may have triggered some sort of protection circuit that will reset itself when you connect a load that is within the supply's limits. Try disconnecting everything from the supply and measure the output voltage. If it goes back to 13V, crank it back down to 12V and try using it again. If the voltage remains low, the supply will require repair (yeah, sure, you betcha) or replacement.

Operating anything at the limit of its specs is asking for trouble. If you are going to buy a new power supply, make sure it is capable of supplying the required power plus about 25-30% more. The price difference between a 320W and a 450W power supply is only a couple dollars and buying the higher power capable one will save you this sort of trouble and expense in the future. A few extra dollars spent up front is cheap insurance. Also, industrial type supplies generally have all sorts of protection built in that the only slightly cheaper "LED" power supplies don't have. If you see a bunch of certifications like UL/CE/TUV on the supply, it is probably a good one. Real Meanwell supplies have all those certifications. I recently bought a new in box 24V 8A Meanwell power supply via ebay for $40. A similar rated "LED" supply would have cost $30. The $10 difference is minor compared to the inconvenience of spending another $30 and waiting for a replacement power supply to arrive.

If your bed heater doesn't get hot enough, get one that's rated to deliver more power/heat. But if you do that, make sure that the MOSFET on the controller board can handle the extra power/current. If it isn't you may have to add an SSR with a heatsink and fan, or you'll end up replacing the MOSFET and maybe the controller board, too. This sort of crap is why buying a cheap printer with the idea of upgrading it in the future is a bad idea. When you change one thing it leads to a whole list of other things that have to change. You would have been better off spending more up front to get something that does what it is supposed to without any upgrades.