With honey, ants love honey.
Since you are running S1's I assume you do not care about efficiency. So I would score up the older non-80PLUS PSUs since these will be cheaper then newer ones.
A stock S1 will use about 370W so you can get a 1200W and power 3 of them with one PSU or get the J4bberwock 2880W setup and run 7 of them off one PSU.