Have an important question on a line output converter for car audio?

I have a stock head unit and a 250 watt amplifier.

I know that I will need a line out converter,

but when I look to find one, there is a maximum wattage rating for them

Is this specified wattage for the output of the head unit, or the amplifier?Have an important question on a line output converter for car audio?
The LOC's wattage rating refers to the output power of the head unit, not the amp. I wouldn't worry much about it; just about any line output converter should be fine with a factory head unit.