Ok, i'm almost finished building a new old PC, i had a old working PSU laying around so i though i can use this, obviously the PSU missed the usual 6 pin model used for PCI express GPU, so i went online i bought one of these

The problem now is that while i'm installing Win7 sometimes the video feed drops for a second and also the PC keeps resetting at the win7 startup, the motherboard is also telling me something about surge protection. I checked with a multimeter and the adapter correctly feed the card with 12v stable; what could the problem be ?