Each Titan X has a 250TDP, at gaming it will have an average 224W, let just say you maxed the 250W since you have 4 of them then lets say it is already 1000w plus other hard-wares on your system plus headroom. In theory you should be fine but maybe you are peeking more than 450w on your other hard-wares. Is the PSU becoming hot to the touch? if its hot does the PSU fan running? The PSU fan should automatically run to cool down the PSU, if it doesn't then you just have a faulty PSU.
Each Titan X has a 250TDP, at gaming it will have an average 224W, let just say you maxed the 250W since you have 4 of them then lets say it is already 1000w plus other hard-wares on your system plus headroom. In theory you should be fine but maybe you are peeking more than 450w on your other hard-wares. Is the PSU becoming hot to the touch? if its hot does the PSU fan running? The PSU fan should automatically run to cool down the PSU, if it doesn't then you just have a faulty PSU.