it's ok. all of them i find are same specs but slightly different model number. either way, this is an old design for old systems not in use anymore. you need the full power on the 12v rail, 42 amps for a 500w unit. your unit has 18 amps and the rest is spread around the 3 and 5 volt rails. at the time this was made systems used a lot of 3 and 5 v power but that has gone away with 12v being the main source for the parts.
the cpu itself is about 100w, the rest of the system is roughly another 100w (the motherboard features, hdd's and so on). that leaves nothing for a gpu at all.
do yourself a favor and replace that old psu and get one designed for a modern system. we can help you identify what is quality based on what is available to you in your area. it's not going to be a $10 psu though for sure. if you have to save up some, then you should do so BEFORE trying to install a gpu. if you're lucky it'll trip the protection and it will shut down. if you are not lucky, then it'll overdraw itself and light itself on fire and possibly take a lot more than your pc with it!!