Question 1

What power connector is needed?

Accepted Answer

It came with the power connector when I purchased it. It's one that has the old floppy drive connector on one end that plugs into this card and an IDE connector for the old school type hard drives on the other end. As long as you have one free IDE style power connector from your power supply you should be fine.

Question 2

is this product support 4TB HDD ?

Accepted Answer

Yes, but also:
That may depend on the manufacturer of the hard drive. You may want to visit each products wbsite for more info. 
The Seagate 4TB HDD is almost Identical to Seagate Barracuda hard drives except the HDD  have more storage capacity and slower spindle. If you have a seagate than the SYBA SY-PEX40045 SATA II should be fine. I have a 1TB Barracuda and have no problems; product works great.

Question 3

It looks like there are four connections, two are sata, what are the others?

Accepted Answer

The power supply comes with the product as shown, with one sata cable provided. the molex cable is the power supply & there would need to be an open sata port from the motherboard to supply the data and expand data supplies.
      On the SYBA SY-PEX40045 SATA II 3.0Gb/s :
Four ports 1) (white) power supply
                 2) SATA data supply from mother board
         3) & 4) Are SATA supplies ports to extra drives etc. that may be needed or as extra for later use

good product for the money but can be damaged fairly easily if not careful when connecting ports especialy the power supply port.

Question 4

looking for two sata expansion ports for two hard drives. would this work?

Accepted Answer

yes

Type	SATA II (3.0Gb/s)
Internal Connectors	2 x SATA II
RAID	RAID 0/1 JBOD
Operating Systems Supported	Windows 7 32/64bit Vista Windows XP Windows 2000 Server 2008 64bit Server 2003 32/64bit

SYBA SY-PEX40045 SATA II (3.0Gb/s) 1:2 (2x1) Internal Port Multiplier

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Model
Brand	SYBA
Model	SY-PEX40045

Item#: N82E16816124049