You can work backwards from the PSU power calculator Utility at the link below. A lot depends on the 12v rail amps. available from your current 300W PSU. In reality you're looking for a Vid card that draws ~100W or less under max load.
If you want to objectively, accurately and scientifically determine what PSU power is required for your Vid card and PC in both watts and 12v rail amps., the forum Utility link below will show you how easy it is to calculate this information and objectively determine which PSUs are quality built, reliable PSUs that can meet your needs. Be advised that the available 12v rail amps. is just as important as the total PSU wattage. You need both to be correct.
Thing is, how many quality 300w power supplies are sold these days? Its likely a generic, or off brand unit that can't sustain rated power anyway. Keep a voltage utility handy when using this P/S and a new video card. Hopefully, if the voltage goes out of tolerance while gaming, the alarm will pull you out of the game before your power supply goes poof. I replaced a motherboard, CPU, and power supply in a customers emachines unit a couple years back, because his kid put in a video card it couldn't handle. When the 12v P/S rail went, it cooked half the stuff using the 12v rail. He had a 300w PSU as well.
its for train simulator 2012 , want top resolution and highest quality graphics , all my specs are good except the graphics card , have HP-141 ELITE , I am willing to upgrade power supply and card , just need to know a sensible combination that is not overly expensive
An HD 6670 will be fine on a 300W power supply (if its a decent quality one - which many aren't at that level). Pretty much any card that doesn't require an external power connector can do it and that's the best one.
HD 5670s are also available low profile but harder to get
also watch out with OEM slim half height cases because
the fan assembly from the card can be a problem to fit in
I had to mod the assembly to make it fit in my Dell slim Desktop
HD 6570 DDR3 vs HD 5670 GDDR5
which wouild you pick?
That is the review I saw
So in May I was shopping for a card for my low pro Dell
but never saw the 6670 LP
That is alright I saved about $30 and really didnt lose too much performance
by going with the HD 5670
for the OP the two choices are the HD 6570 and HD 5670
since both are offered in Low Profile (half height)
I run the 5670 on a 280w PSU and no problems (so far)
I have read of the HD 5670 running on 250w PSUs
and the HD 6570 is similar in power draw
definitely under 75w since that is limit of PCIe slot by itself
the HD 5670 maxes according to AMD website at 64w peak wattage
I just wouldnt have too many HDs opticals PCI cards with the card
I have 1 optical 1 HD 2 pci cards (sound and tv tuner) E4500 C2D
and according to PSU calculator require @270
one thing is that the Dell PSUs wattage is rated at continous max
not peak max so the 280w is equal to about a 350w peak
OP should look at PSU and check ratings on label
particulary 12v amperage