Power cables are a basic component of electrical systems; one end plugs into some sort of electrical device, and the other end plugs into a power source such as an outlet. The cable then allows electricity to safely travel to the device to power it and enable it to perform its desired functions. There are different types of power cables carrying different designations such as "SJ" or "SJO."
The "S" in "SO" means "stranded" or "service wire." Cables so designated are suited for heavy duty industrial tasks requiring 600 volts. The "stranded" refers to the cable's core being composed of multiple strands of conductive materials instead of a solid core. The "O" means that the coating on the outside of the power cable is oil resistant; cables with "O" in their designation can safely be used in environments in which they will be exposed to oils, such as in machines with engines.
An "SJO" power cable shares all of the characteristics of an "SO" cable; they are strong cables with a stranded core and able to resist oil-laden environments. The "J" in the designation qualifies the "S" -- "J" designates "junior service." An SJO cable is still stronger than a household power cable, and its core is comprised of strands, but it is only rated for use at 300 volts, half that of regular "S" cables. This makes these cables designed for lighter work than their more powerful 600-volt counterparts.
Both SO and SJO power cords can be found at a variety of online and brick-and-mortar retailers. The "J," or "junior," rated power cables tend to be a little bit cheaper due to their lower-rated specifications. There are also several other features that may be assigned to a power cable, such as "W" meaning the cable is weather-resistant or "T" meaning the cable is coated in heat-resistant thermoplastic. If you only need "SO" or "SJO," you may want to avoid these extra features as they may increase the price of the cable.
When deciding which power cable is best for your needs, refer to the documentation for the electrical device that needs power. It will list the specifications for the electrical motor including the power input required to turn the motor on. Purchase the appropriate cable depending on the amount of power needed. Make sure that the cable you purchase has "O" in its designation so that it can be used in areas such as roadways where oils tend to build up.