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, training with hand grippers won't help you execute barre chords. Firstly, time spent squeezing grippers is time that you could be using to actually practise barre chords. Secondly, the physical action is markedly different and not about finger placement and subtleties of pressure. But hey, you could end up with a really impressive handshake, and all the other musicians will ask you to carry their gear. It's early days; hang in there and your barre chords will improve.
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.