Temperature drops during printing

It have been about six months or more since I got my first 3d printer and I only printed one ugly part
The problem: when I start printing the temperature drops enough so the extruder doesn't work anymore. I don't know where the problem is. My printer is a Aurora 605z using a Reprap melzi 2.3 board and Repetier host as software(not the latest version). The temperature I use to print is roughly about 250°C with ABS
If you could help me fixing this would be awesome
Thank you in advance

Temperature drops during printing usually indicate a power supply problem. If the power supply that supplies the motors and heaters is working too hard it will produce lower voltage which will quickly cause the temperature of any heaters to drop. Check the power supply voltage with the machine idling and as it operates. If the voltage drops by much, you may need a new, higher current rated supply. It's also a good idea to check the wiring between the extruder heater cartridge and the controller board. If you have an intermittent connection you need to fix it.

And where can I find a new and more powerful power supply?