It's highly recommended NOT to use any adaptors.
If your PSU doesn't have the correct connectors then it's time to buy a new PSU. That is the bottom line to be safe.
You could end up cooking the PSU, the NEW card and or your whole PC.
Nothing wrong with the card, it would be the PSU in question doesn't have the correct connectors. That means it's either too old, not enough power and or very low quality.