A system can produce a suitable voltage for powering the memory modules plugged into the memory module slots of a motherboard. A power-good signal is issued when the motherboard is powered up. A power safety device on the motherboard then issues a 2.5V to the memory module slot. If DDR DRAM type of memory modules are not detected after a while, the power safety device will turn off the 2,5V supply and provide a 3.3V, which is suitable for SDRAM type memory modules.This invention avoids sending a 3.3V to DDR DRAM modules, thereby burning the memory chip. The presence of DDR DRAM modules can be detected by a general-purpose purpose input/output port through accessing the recorded data in the EEPROM of the memory module. Alternatively, memory module type can be determined by sending out a low-current pulse signal to the memory module slot. Hence, a suitable voltage source is automatically provided to power the memory modules in the slots.