If your power isn't very good, I recommend buying a UPS. It will protect your power supply during brown outs and spikes. Also it will keep your miner running during very short power blips.
I had two power supplies blow.. my computer would keep restarting as I get like 10-20 brown outs a day.. UPS = golden fix. Gotta keep that power smooth!!!
On miners and UPS's... Miners do NOT like yer normal PC stand-by UPS's. Been there, tried that with several different makes. Even with a miners PSU at 1/2 load every one I tried caused the miner to hang when they switch or adjusted the voltage. Reason is the relay switch transfer time which for most UPS's is spec'd at <10ms. That blip is long enough to often cause a big enough dip in the 12v output to lockup the controller.
If you are going to uses a UPS is MUST be what is called a on-line UPS. Less efficient as they are always 'on' changing AC>DC>AC but there is zero transfer time. For several of my S4's and S2's I use
http://www.cyberpowersystems.com/products/ups-systems/smart-app-ups/paragon-series/ol2200rtxl2u.html Pricey? Yes. However, are rock-solid.
btw, the s2's & 4's are the only ones on UPS's. When spiked (well, dipped really) they can be (are) the most susceptible to the sd card getting munged.. S3's and s5's just hang so the majority of the farm is not on UPS's. Waayyy too expensive to do that.