you people really need to stop trying to cram a v8 engine into a 69 beetle.
you can not use a NVidia Geforce GTX Titan Z with a HP Z600 Workstation (Dual Xeon X5670, 32GB Ram, 1 SSD, 1 HD)
replace the system with something that was designed for that card/power draw like a z820/z840 with the optional 1250 watt pwr supply
if you want to damage the card and the z600, by all means install it and then watch the magic blue smoke appear shortly after power on. the point i'm trying to make is that some things just do not play nicely with others and this is one of them
if a z8xx system is out of your price range then try looking at other systems, on ebay. a z420 with a power supply converter cable to use a normal ATX supply can be bought on amazon just be aware that the power supply will most likely need to be in the 750/850 watt range for a single cpu system and 850 or more for a dual cpu system. and one last thing tier 1 pwr makers 750 watt supplies cost around 80/100 dollars....advoid the ebay no name $30.00 800 watt supplies as they are crap and will not actually be able to do 850 watts much less 300 watts.