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400W is fine as the 1GB GT 610 only requires a 300W PSU with 22 amps on the +12V rail and no additional pcie power dongle, the PSU suggested by myself was based on the fact that lower output PSUs actually cost more than the 400W, SFX example here and ATX PSU here
From the PSU I can see a power lead going to these items Main board, DVD and HDD.
That will be correct + you will also have the following;
1 x4-pin ATX 12V power connector for the CPU.
1 X24 power connector for the MB itself.
Couple of tips for you, before swapping out the PSU, take some pictures of the connections inside of the case or attach labels to the present PSU leads identifying which component they connect to then use them for comparison when connecting up the new PSU and please read my canned safety info below before starting;
The following checks require the computer case to be opened so take the following safety precautions 1st, disconnect any attached hardware such as the keyboard and printer etc, disconnect the power cord from the wall socket, press the case power button for 10 seconds or so to get rid of any residual charge in the system, remove the side of the case, be sure to take anti static precautions before touching anything inside, you can do this by touching a bare metal part of the case or the PSU.
If unsure on anything along the way post back and let us know.
You are welcome btw