Older hard drives wont have an 8 pin cpu connector for the mb . They will just have the 4 pin . Someone on here said that even mb's with 8 pin sockets run with a four pin plug from the psu inserted . But Im not havent tried that and cant confirm or deny ...
Definitely older psu only have 20 pin main power connectors and new mb's take 24 pin .
Then theres things like SATA power connectors [ can buy adapters from the molex connectors ]
And 6 and 8 pin power connectors for gfx cards .
Its worth spending the money on a decent corsair , seasonic , antec etc to be sure