I'm told 24 to 20 is fine(no surprise) but 20 to 24 is "less than ideal". Whether that's because it doesn't properly power the PCI-E bus or just because it doesn't properly implement twin 12v rails or not I do not know. I do know I've seen several learned support reps expressing reservations about using 20pin to 24pin adaptors though they're never very specific as to exactly what the consequences will be long term. I assume it'd simply be reduced stability. I did notice that my usually robust 400w FSP 20pin unit was unable to handle my nF4 board with only a single 6600GT when I began overclocking botht he vid card & the CPU to max levels. I was not using an adaptor however, just leaving the additonal 4pins on the ATX header blank, though I did plug the remaining 3 power connections on the board.