AC = Alternating Current (simplified explanation)
The 110 or 120 is just the measure of the voltage you get.
As far as your concerned it is the same. The power company decides what actual voltage you receive. It was originally 100 then went to 110 then 120 and in some places in the U.S. it is up in the 125 to 130 volt range. It is all about the demand level in your area. It is sort of like increasing the pressure on a water line to allow more delivery. It is actually pushed in 440 or 460 and split ( the power legs) into 220 or 230 and then split into 110-120 etc.
Not something you can control. Any device labeled as such is fine. I.E. if you buy a 110 device just plug it into the 110 outlet not the 220. (thats why they have different plugs so you can't)
The SO is a NEC (National Electrical Code) code for the insulation layer(s) of the flexible electric cord
goes so meting like this:
S = Service Grade (also means extra hard service when not followed by J, V, or P)
J = Hard Service
V = Vacuum cleaner cord (also light duty cable)
P = Parallel cord (also known as zip cord) – Always light duty
E = Thermoplastic Elastomer (UL/NEC designation ONLY)
O = Oil Resistant*
T = Thermoplastic
W = Outdoor-includes sunlight resistant jacket and wet location rated conductors (formerly "W-A")
H = Heater cable
VW-1 = Flame retardant
FT2 = Flame retardant
so...S-O cord is ...Service grade-oil resistant and since it only has one O it means only the outer jacket is, not the inner wire insulation layers are graded as such.
hope that helps
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