Hello, My MacPro 5,1 power-supply is making a buzzing sound. I have already tried cleaning it out, but the sound still comes and goes. I'm thinking of buying another power supply to have a backup as I use my system for work. The model on my PSU is dps-980bb-2. While online I did see some units without the -2 at the end of the model number. Are they compatible with my system? Also is Delta or the ACBell better? A bad power supply wouldn't cause any UI lag would it? I might have to upgrade my GTX 680 to fix that, but that's on another topic. Thanks!