It depends on your jurisdiction. Some products fall under the Consumer Product Safety Act, others falls under different regulations. In Canada marks are required, in the US it depends on where you are and where you're installing it e.g. is it for home use or a hospital's internal network?

https://electronics.stackexchange.com/questions/10639/is-ul-...

If your house burns down using an uncertified product, your insurance company may not also cover the claim. Personally I prefer to run electronics that I know are tested to not burn down my house or electrocute my children when they fail.