POWER RACK - Also known as a power cage or squat cage, this is a popular piece of weight training equipment that is mainly used as a rack for freeweight barbell exercises. Unlike a Smith machine or any weight machines, it doesn't impose movement restrictions. The bar holders can be adjusted to any height on the rack, so that you can set the bar at various heights depending on the height you need to unrack the bar at for exercise you're performing. The safety bars are the longer bars extending the entire depth of the rack and are set to a position just under the bottom of your range of motion, to catch the bar in case your strength gives out.
SQUAT RACK - Squat racks are built with an open-front design, whereas power racks have four uprights keeping the bar from falling forwards or backwards out of the rack. Squat racks may or may not include safety bars to catch a failed rep, and the safety bars may or may not be adjustable. Some are squat stands, which are two independent space-saving stands that can be moved into a closet when you're done with your workout.

These squat racks for sale are also used for bench presses and a variety of other pressing and pulling exercises. Some are also called power racks. While many squat racks for sale here have fixed-height safety bars, or none at all, power racks are completely adjustable.
Depending on the height of your bench, you'll likely want to set the safety bars a little lower than you would for squats. You'll figure it out. The idea is to set the sefety bars just a little lower than the bottom of your range of motion so that it will catch the barbell if you fail a rep. It increases of the safety of bench pressing, squatting, and other presses such as shoulder presses and incline presses. These racks are also used for rack pulls, a deadlift-like exercise with a shorter range of motion and heavier weight.
Most power racks include a pull up bar. Some power racks also include other optional attachments such as a lat pulldown machine. Over the years, people have come up with many exercises that can be performed in a power rack with additional pieces of equipment, such as dips and sit-ups.