Power off, remove all memory and reinstall only the original Dell memory sticks and then retest. If the power issue does not happen, the fault was the new memory. If it still happens, run the power supply self test.
* Look at the back of the power supply for a black button and an LED * Press and hold the black button in * If the LED stays green, the power supply has passed
If that passes, then perhaps the motherboard is faulty.