Ah the good old and reliable ANTMINER S3+
I remember at stock speeds that beast used around 400 Watts almost. So 200 Watts each side. So the PCIe connector will be fine however...
DONT USE THE MOLEX TO PCIE converter because it will cause it to melt. You really are better off getting another PSU since that one is not adequate for the S3.
I concur on the danger of using that 430 watt PSU....I used a Corsair CX600 watt with each of my S3+ & had no issues at all
They were about $50 each from Newegg many years ago