What do the voltage and current on the splayed power line mean?

This refers to the rating. This means that the voltage that this line can withstand is 125V, 2.5A That is to say, when the current and voltage are less than this value, the operation is safe, the insulation of the conductor will not be broken down, and the line will not be burned out. Beyond this value, it may not be damaged, but the quality is not guaranteed.