Question: First of all I just started doing barre chords after learning ordinary non-barre chords. Problem is they don't sound so well, so my question is, will training with hand grippers help me achieve this? Because I've been applying equal pressure and they still sound a bit off, only a bit off.

Answer: 
No. Simple answer. Your hands could be stronger than a weightlifter's and still not play barre chords, or any other chords, well.

Actually, hardly any finger strength is needed. Putting fingers as close as possible to the fretwire helps, accurate fingering helps, and a good action helps. If the strings are a long way above the fingerbaord, strength will help, but a better solution is to improve the action, or change guitars.

If any muscles help, it's the arm muscles, as they should be used a little as levers, using the thumb as a fulcrum point - which also doesn't need to be clamped to the neck.
Grippers (hand squeezing exercisers) won't get you anywhere. It may sound trite, but the best exercise for improving your barre chords is to play barre chords. Work on correct technique and position, and eventually you'll see marked improvement. You can try to focus on 'power chords' initially (i.e. just the lowest 3 notes, the root, 5th and octave) but don't let this become a crutch. If you're like me, it's the notes that ought to be fretted by the index finger that are likely giving you trouble, but soon you'll come to 'grips' (forgive the pun) with the required touch to properly voice the notes and whole new worlds of playing joy and success will open up for you. 

Don't worry about voicing that high E string when playing an 'A' shape barre chord, almost no one gets their ring finger to back-bend sufficiently to let that high E string ring out while playing an 'A'-shape barre chord (eg x57775 for a D chord, most players wind up playing x5777x for this, unintentionally muting that high E string.) 

One last thing, don't fall into the bad habit of trying to 're-inforce' your index finger by overlapping your middle finger on top of it. You're gonna need that middle finger elsewhere soon enough, and unlearning bad habits is much harder once they're ingrained. 

Have fun and keep practicing.