The main difference between S.I.T. Power Wound Nickel and Power Steel Stainless electric guitar strings is the material used for the wound strings.
Power Wound Nickel uses nickel-plated steel wrap wire. Nickel-plated steel is a popular all-around electric guitar string material because it provides a balanced combination of brightness, warmth, clarity, and versatility.
Power Steel Stainless uses stainless steel wrap wire. Stainless steel generally produces a brighter, more cutting tone with pronounced attack, clarity, and high-end presence.
If you're looking for a balanced and versatile electric guitar string, Power Wound Nickel is a good starting point. If you want more brightness, bite, and presence, Power Steel Stainless may be the better fit.