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: 
It turns out that strength is not what is needed to improve your ability to finger barre chords, or any chords. It's mostly about precise placement and using the minimum amount of force to hold it down.

It's not necessarily that equal pressure is correct. You just need the right amount of pressure for each fret and string.
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.