Equipotential lines perpendicular to E field lines.

Electric field and equipotential applets link

Work done in uniform field

Electric field strength,
E= 1600 N/C.
AB: No work as they are along equipotential lines.
AC is the same as BC as E= V/d , V = Ed
Work = q (Ed)= (1uC)(1600x0.08m) = 128 J
The work is independent of the path whether A to C or B to C.
A positive charge moving form A/B to C would work done against electric force. A negative charge moving from A/B to C would have work done on it by electric force. The positive charge would have increase in EPE = 128J .
A negative 1uC moving from the same locations would have decrease in EPE = 128J .

Work and Potential difference

Note: The analogy is good but can you detect an error in the uniform electric field diagram. The larger distance of the negative charge away from the negative plate will not give rise to more energy stored.

Work W=qV where q is the charge moved between 2 pts where the potential difference is V. If you move 1 C from a to b where the potential is 10V and 12 V . The work = (1C) x (12V-10V) = 2 J. Energy conversion : The KE of the charge reduce by 2 J and the EPE increase by 2 J.
If the same charge returns from b to a : The PE decrease by 2 J and the KE increase by 2 J .
For a negative 1C : a to b : PE decrease by 2 J and KE increase by 2J and vice versa for b to a.
Therefore : A positive charge at rest would move from high to low potential (just as water flows downhill). A negative charge at rest would move from low to high potential ( there is no analogy in gravitational field)

Positive and negative potentials

A different view of potentials. pic taken form stlawu.edu
A positive charge moving towards the negative charge will be falling towards it whereas towards the positive charge will be a uphill task.

Electric potential of a point charge

A positive charge has a positive potential and vice versa. The potential V= kq/r. If q is negative then V is negative. If there are more than one charge in the vicinity , just add up all the potentials , If q1 is positive and q2 is negative , the total potential V is V1+(-V2).
electric potential visualisation taken from cs.princeton.edu