What is "foldback short circuit protection" in a power supply?

I am looking at buying a 24V power supply. Two of the options are these:

The first offers "foldback short circuit protection" and "overvoltage protection," but it is $85 dollars. The second is much cheaper but does not mention these.

What are these types of protection, and how important are they? Are they worth an extra ~$50? Thanks!

Answer

overvoltage protection: protects the input from exceeding the specifications, this would 'attempt' to protect the device from a voltage surge on the DIN rail. There may also be some protection on the output.

foldback short circuit protection: is a method used in power supplies to protect them from over current situations such as shorting out the output with a wire or attaching too much equipment to the power supply.

With normal (high side) current limiting there is a hard current cap that the supply is limited to to protect it. As the load resistance approaches 0 the current is limited to a fixed value and the voltage begins to drop. This can cause a large amount of power dissipation in the supply.

With foldback protection, as the voltage drops the current limit also drops fairly linearly. This provides safer protection from short circuits as a "really bad" short will result in very little current draw so the supply won't be sitting there baking at max current.

overvoltage is what it is, the response time and current carrying capabilities of basic overvoltage circuits aren't going to save you from lightning strikes but may protect you from small screwy surges from the power company.

A dedicated surge/power smoothing device at the source of the DIN power is a better option.

foldback style over current protection is simply better/safer than only having high side current limiting.

In both cases they are reliability/durability features, the question of if its worth it, depends on how critical downtime is for the equipment your connecting to it.