Current Card: Nvidia gts 240()
Motherboard: Studio XPS 8100 - at least that's what the system model listed in the system information program is ...
Processor: Intel i7 Processor 860 (2.80 GHz, 8MB)
Choice of card : Nvidia GTX 460 (1st Choice) () or Nvidia GTX 550 ti ()
I only have a 350W psu but my current graphics card says it has a minimum system power requirement of 450W and uses 120W of power under full load. The nvidia gtx 550 ti needs has a minimum system power requirement of 400W and uses 116W of power under full load. The nvidia gtx 460 has a minimum system power requiremnet of 450" but uses 160W of power under full load - substantially more than my current one. Would my XPS have enough power to support the gtx 460? I think it could and am pretty sure it could support the less power intensive 550 ti but I am not sure.
I am not sure if a new graphics card would fit. Both new cards are shorter and the same height as the gts 240 but they are dual-slot instead of single-slot. Does this matter or what?
If a card uses too much power it could shut down or short your computer. If the cards are too long for your motherboard/case then it won't fit. So yeah it matters.
If your current graphics card uses more power "under full load" than the 550 ti, it should work if the old one did without a hitch, but that's up to you. Might want to upgrade psu anyway, if it's not 80-plus and has anti-short powers.
Aside from telling you what you already know..
I suggest finding out the exact length of what card you want to use. Then measuring your motherboard/case yourself to find out if it will fit.
it is not as important as to what wattage your psu is but how much amperage it supplies to the 12 volt rail.
to use a 460 with 160 watt draw would mean you PSU need to supply 13.4 amps to power that.
also you would need to add in the 95 watts your cpu uses, 10 watts for each HD, 8 watts for your chipset and 4 watts for each stick of RAM.