Hi there, i wanted to know if the 8600 GT will run fine on the stock china made 400W PSU that comes with the cabinet?

you´ll be ok

Amps on the 12v line? It should work for a while, psu will start to degrade though

What do you mean by amps on the 12V line? i dont have much knowledge about PSUs

There should be a label on the PSU that list the information he was asking for.

my bro runs a 4850 on a 430w antec for couple months now

and what about a 9600 GT on a 400W?

depends what 400w you have tbh , a 400w named brand like a corsiar or tagan etc would be fine , but if its a no name brand cheapy then no it wont. it varies soo much from psu to psu. the stock case ones tend to be substandard and i wouldnt risk running either of those cards you mentioned on it tbh.