Generally, if your PSU doesn't have the appropriate connectors, using it is a bad idea. Connectors exist, but unless the PSU is a quality unit and the only reason it lacks some connectors is it's age, the connectors/adapters are a bad idea.
Your PSU sounds like it's just a generic PSU, labelled 500W which, in all likelihood is a blatant lie. That model name shows up as branded by both Dynex and Apevia........which is not a good sign.
http://www.tomshardware.com/forum/id-2547993/psu-tier-list.html
Avoid IMMEDIATELY. These units are highly unsafe to use. No such protections added, very thin gauge wiring used, false advertising and too much to list. Reference to a higher tiered unit for a better, money saving and a much safer unit. For your safety's sake, please don't order or pick one up for use in your system. These units are a potential fire hazard and could even kill you, let alone your system.
Apevia
Dynex
Considering the GTX 570 is a 219W TDP card, running that on any generic (junk), dated PSU with adapters etc is just asking for trouble.
Best case, nothing works.
Worst case, the PSU explodes.
Buy a new, quality PSU if you want to run a 570. Simple as that.