The 7750 does not need a PSU connector because it draws all of its power from the PCI-E lane (which is limited to...80watts or so if I'm not mistaken) so I'm assuming any PSU can handle it. Your other components don't require much power either so there shouldn't be a problem.
Bear in mind that there is a version of the 7750 that needs a 6pin power connector.
I am planning to buy the SAPPHIRE HD 7750 1GB GDDR5 http://www.sapphiretech.com/presentation/product/?cid=1&gid=3&sgid=1159&lid=1&pid=1454&leg=0
It does not state any requirement of 6-pin connector in the system requirement.
PCI Express® based PC is required with one X16 lane graphics slot available on the motherboard.
Certified power supplies are recommended. Please refer to: http://support.amd.com/us/certified/power-supplies/Pages/listing.aspx
1024MBMinimum of system memory.
Installation software requires CD-ROM drive.
DVD playback requires DVD drive.
Blu-ray™ / HD DVD playback requires Blu-ray / HD DVD drive.
To support 3 displays, one of the monitors has to support DisplayPort.
400 Watt Power Supply is required.
So I guess I will be ok even under peak load ~75 Watt power consumption by the card.
I was just looking for other users to comment who uses Chinese make PSUs for running HD 7750 , so that I can learn from their experience if it is dangerous or not.