Earn enough points using Stealth Grid to cross the points threshold and this challenge will be completed. Any difficulty, enemy, or map will count towards this challenge.
It's not always clear how the points are awarded for using this skill. When a power cell is used, +20 Support will show on screen. This XP award is for the player that activates the power cell. Any nearby allies and/or friendly constructs like an Assault Turret or a Remnant VI that Stealth Grid affects will also award an additional +20 Support. However, those only appear one at a time after the original XP award fades. Activating a power cell in a group of four teammates will ultimately award +80 XP (4x +20 Support) for each power cell used. Any constructs affected can increase this number even higher.
It is not required to wait until Stealth Grid wears off before activating a new power cell. Each activation awards XP. It is possible in a tight group of allies to rapidly fire off all of the power cells available and quickly rack up points for this challenge. The only issue is that it takes a very long time to show each +20 Support award on screen as each award has to wait until the prior one fades away.