Looks like a normal PCIe power adapter cable. You use this when your power supply doesn't have the proper PCIe connector. And yes you will be safe with using it, just plug in both molex plugs and plug it into your video card and you'll be fine. With your bad luck I'd say you should consider what PSU you are using. If it is low quality, you are running the risk of having your rails spike and overvolting yer components. Even if(and especially if) you bought the computer as one from a big manufacturer, I'd say the chances of getting a shitty and unsafe PSU are pretty good.
Core i7 920 @ 3.8Ghz | 6GB OCZ DDR3 8-8-8-24 @ 1600mhz | eVga x58 Mobo | 2 x eVga GTX 460 SLI | Intel X25-M + 3x Seagate + WD Black = 2.75TB | X-Fi Titanium | PCP&C Silencer 750 | G15 KB | G5 Mouse | G35 Headset | Z-5500 Digital | Samsung T260HD
