Difference between electric potential energy and electrostatic potential energy?

We know that electrical potential energy is the work done in bringing a set of charges from infinity to a point opposite to electric field.

And in electrostatic potential energy there is only one difference that here it is only one positive charge not a set.

My question is that how their units are same, i.e. volt.

According to me volt is the SI unit of the electrostatic potential energy as one volt is work done per unit charge. So there is one unit charge not so many, so we should not consider electrical potential energy.