I am sure there is nothing in the power plug, I have taken apart several of both types of LED light strings, and there is nothing in the plug except for fuses. I am guessing that maybe the internal diode resistance is enough to limit the current when there are enough bulbs to almost reach 120V just using the internal diode drops. I will have to count how many bulbs are in series in each of the two types of lights and see if that shows any pattern

I rebuild old Christmas light (filament and LED) sets that are given to our local recycle center and then donate the lights to local charities that have resale facilities, and I have several strings of each type in my rebuild boxes so that is mostly a matter of getting to it. I'll post the results after I have done my research.