Every PSU is different. for example some PSU's have a separate Power Rail dedicated for PCIe devices (video cards) some share the same amount of power and is just dispersed to what is connected in no dedicated fasion. I have an OCZ Powerstream 600w with 2 dedicated 6+2pin PCIe connectors but my Coolermaster Elite Power 350w has no PCIe connectors. I can still use (which i have done while i wait to build my new computer) is use a Dual Molex Y connector to single PCIe 6pin. (for my 5750 XFX card) its a low power consumption card paired with my 65w i3-2100 so it works perfect.
Diffrence between connections Molex and SATA are around the same voltage and all peripheral connections are sharing the same power so therefor the connectors are just different, so when looking at extension cables, you need to buy extensions for the specific devices your connecting to. YES you can buy adapters for Molex to SATA if you need more SATA power connectors .
Hope this helps.
