Power Girl is the cousin of Kal-L, the Superman the pre-Crisis Earth 2. She is essentially the Earth 2 version of Supergirl.
Her 1st appearance was in All Star Comics #58 in January 1976. Her character was created by Gerry Conway, Ric Estrada, and Wally Wood.
Essentially, she has the same powers as Superman such as flight, superhuman strength, super speed, x-ray vision, telescopic vision, heat vision, freeze breath and super-hearing.
The biggest different between her and Superman, besides the fact that she is a girl, is because she is originally from Earth 2, kryptonite from New Earth does not affect her. The only real vulnerability she has is magic.
Ms. Marvel was created by Roy Thomas and Gene Colan. Her character 1st appeared in Marvel Super Heroes #13 in March 1968.
Her alter-ego, Carol Danvers, was originally an officer in the United States Air Force and friend of Dr Walter Lawson, the alter-ego of the Kree Captain Marvel.
She was caught in the explosion of a Kree device which is how she got her powers: superhuman strength, endurance, stamina, and flight. She also has the ability to discharge explosive blasts of energy from her fingers and can absorb other forms of energy which amplify her powers. She has other skills such as espionage, piloting, hand to hand combat and marksmanship.