Wrong voltages with DAC MCP4725 driven by Mega250

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10

I can not confirm your issue. When I run your code with the 0x60 address of my mcp4725 I see expected results.

//#include <Wire.h>
#include <Adafruit_MCP4725.h> // na install steeds IDE heropenen

Adafruit_MCP4725 dac;
// after scann.: I2C device found at address 0x60  !
//               I2C device found at address 0x61  !

int lookup = 0;//variable for navigating through the tables
int address=0x60;
int readV=A0;
const int numb=8;
int simpleTab[numb] = 
{
  200,400,800,1000, 2000,3000,4000,4095 // 
};
float v[numb];


void setup()
{ pinMode(A0,INPUT);
  //Wire.begin();
  dac.begin(0x60);

  // Set A2 and A3 as Outputs to make them our GND and Vcc,
  //which will power the MCP4725
  pinMode(A2, OUTPUT);
  pinMode(A3, OUTPUT);

  digitalWrite(A2, LOW);//Set A2 as GND
  digitalWrite(A3, HIGH);//Set A3 as Vcc
  Serial.begin(57600);
  Serial.println();
}
//---------------------------------------------------
void loop()
{
  //Wire.beginTransmission(MCP4725_ADDR);
  //Wire.beginTransmission(address);
  //Wire.write(64);                     // cmd to update the DAC
  dac.begin(0x60);
  Serial.print("address(hex)=");Serial.print(address,HEX);
  Serial.print("  lookup=");Serial.print(lookup);
  Serial.print("  lookupWa=");Serial.print(simpleTab[lookup]);
  //Wire.write(simpleTab[lookup] >> 4);        // the 8 most significant bits...
  //Wire.write((simpleTab[lookup] & 15) << 4); // the 4 least significant bits...
  dac.setVoltage(simpleTab[lookup], false);
  //Wire.endTransmission();
  delay(10);

  Serial.print("  an.value=");Serial.print(analogRead(readV));
  v[lookup]=analogRead(readV)*5.0/(float)1024;
  Serial.print("  voltage=");Serial.println(v[lookup]);
  delay(3000);
  lookup++;
  if (lookup==numb) lookup=0;
  //if (lookup ==1) lookup=0; else lookup = 1;// (lookup + 1) & 511;
}

address(hex)=60 lookup=0 lookupWa=200 an.value=48 voltage=0.24
address(hex)=60 lookup=1 lookupWa=400 an.value=99 voltage=0.48
address(hex)=60 lookup=2 lookupWa=800 an.value=198 voltage=0.97
address(hex)=60 lookup=3 lookupWa=1000 an.value=249 voltage=1.22
address(hex)=60 lookup=4 lookupWa=2000 an.value=499 voltage=2.44
address(hex)=60 lookup=5 lookupWa=3000 an.value=750 voltage=3.66
address(hex)=60 lookup=6 lookupWa=4000 an.value=1002 voltage=4.89
address(hex)=60 lookup=7 lookupWa=4095 an.value=1022 voltage=4.99

I would remove the dac.begin() from loop(), but that does not appear to be the cause of your issue.

It would appear that you have a wiring rather than code issue, or perhaps a defective module.