Some motherboard producers add a “+” symbol to the specification of supported memory types. Motherboards can have in specifications a “+” symbol for RAM. It is a bit confusing. What does “+” symbol mean for DDR4 RAM ?
The “+” symbol in motherboard specifications indicates that the motherboard supports RAM with a frequency over 3000 MHz. Actually it means that the motherboard allows the RAM to be over-clocked. You will have to increase the voltage or timings to get a higher frequency.