Your indentation continues to be lousy - you'll lose marks.
Code:
#include <stdio.h>

int main()
{
  int times = 1, type;
  double power, cost, TotalPower, TotalCost, max = 0, min = 0, current, voltage;
  do {
    printf("\nRecipient #%d information:\n", times);
    printf("\nInsert current > ");
    scanf("%lf", &current);
    printf("\nInsert voltage > ");
    scanf("%lf", &voltage);
    if (times == 1 && current == -1 && voltage == -1) {
      printf("no recipient information is inserted ");
      return 0;
    }
    printf("\nEnter Consumption Category:\n");
    printf("1 = Residential\n");
    printf("2 = Commercial\n");
    printf("3 = Agricultural & charities\n");
    printf("4 = Government \n");
    printf("5 = Industrial \n");
    printf("6 = Private Educational and Medical\n");
    scanf("%d", &type);
    switch (type) {
    case 1:
      power = current * voltage / 1000;
      printf("Power =%.2lf kilo watts\n", power);
      if (power > 6000) {
        cost = (6000 * 0.18) + ((power - 6000) * (0.3));
        printf("The cost = %.2lf Rs\n", cost);
      } else {
        cost = 6000 * 1.8;
        printf("The cost = %.2lf RS\n", cost);
      }
      break;
    case 2:
      power = current * voltage / 1000;
      printf("Power =%.2lf kilo watts\n", power);
      if (power > 6000) {
        cost = (6000 * 0.20) + ((power - 6000) * (0.30));
        printf("The cost = %.2lf RS\n", cost);
      } else {
        cost = 6000 * 0.2;
        printf("The cost = %.2lf RS\n", cost);
      }
      break;
    case 3:
      power = current * voltage / 1000;
      printf("Power =%.2lf kilo watts", power);
      if (power > 6000) {
        cost = (6000 * 0.16) + ((power - 6000) * (0.20));
        printf("The cost = %.2lf RS\n", cost);
      } else {
        cost = 6000 * 0.16;
        printf("The cost = %.2lf RS\n", cost);
      }
      break;
    case 4:
      power = current * voltage / 1000;
      printf("Power =%.2lf kilo watts", power);
      if (power > 6000) {
        cost = (6000 * 0.32) + ((power - 6000) * (0.32));
        printf("The cost = %.2lf RS\n", cost);
      } else {
        cost = 6000 * 0.32;
        printf("The cost = %.2lf RS\n", cost);
      }
      break;
    case 5:
      power = current * voltage / 1000;
      printf("Power =%.2lf kilo watts\n", power);
      if (power > 6000) {
        cost = (6000 * 0.18) + ((power - 6000) * (0.18));
        printf("The cost = %.2lf RS\n", cost);
      } else {
        cost = 6000 * 0.18;
        printf("The cost = %.2lf RS\n", cost);
      }
      break;
    case 6:
      power = current * voltage / 1000;
      printf("Power =%.2lf kilo watts\n", power);
      if (power > 6000) {
        cost = (6000 * 0.18) + ((power - 6000) * (0.18));
        printf("The cost = %.2lf RS\n", cost);
      } else {
        cost = 6000 * 0.18;
        printf("The cost = %.2lf RS \n", cost);
      }
      break;

    default:
      printf("Incorrect Catrgory ! program will stop now ! ");
      return 0;
    }
    if (current == -1 || voltage == -1)
      TotalPower = TotalPower + power;
    TotalCost = TotalCost + cost;
    if (cost <= min)
      min = cost;
    if (cost >= max)
      max = cost;
    times += 1;

  }
  while (!(current == -1 && voltage == -1));
  printf("\nthe total power is : %.2lf \n", TotalPower);
  printf("\nThe total cost is : %.2lf RS \n", TotalCost);
  printf("\nthe min is : %.2lf\n ", min);
  printf("\nthe max is : %.2lf\n", max);
  return 0;
}
Some of your variable names are meaningless, again - marks lost.
> printf("\nRecipient #%d information:\n", times);
Replace 'times' with say 'customerNumber'.


> THE problem is i have to use the switch here and the function make this more difficult
Where exactly does it say in the PDF that you have to use a switch statement?

Sooner or later, you're going to have to start dealing with functions. Putting everything in main() just isn't a sustainable approach.


Study this latest addition to your code.
Code:
    if (current == -1 || voltage == -1)
      TotalPower = TotalPower + power;
    TotalCost = TotalCost + cost;
The scope of the if statement is only the next line.
Do you really mean to calculate TotalPower on the very last iteration?