2nd PSU to GPU shuts off after 40 minutes

[SYM-J]

So the wife keeps stealing my PC to play her sims 4.  I got tired of it so I decided to hook up my older Dell PoweredgeSever to an extra Graphics card I have (a EVGA 660Ti Signature 2) and let her play on that.  I just got everything together yesterday and when I was testing it everything was fine games ran great at 1080p...  I did have to use a 2nd PSU to power the Graphics card since the server's psu couldn't push enough Wattage; so I used a simple jump cap on the 24 pin connector to short out the PSU to turn it on without being connected to a MoBo. The process I'm using to turn on this is...  1) Flip on the extra PSU.   2) Power up the Server.  3) it loads up fine (except the GPU does not out put any image until ot loads into windows)... Everything comes up and works fine until about 40 minutes later when she is playing her Sims and then the PSU will just turn off.   Anyone got any clue?  I don't think  its because of overheating, the PSU is completely open Air and the GPU doesn't get above 40° C in the 40 minutes its on.