Yes.
If you have a thick enough cable with a strong enough PSU, 300W per hashing PCB with 1 PCI-E plug will work but if your wire is not thick enough or PSU is not strong enough to push that much electricity, then you have to use all 4 PCI-E plug
often time with cheaper/discounted PSU, you have to use all 4 PCI-E connectors!
just a quick question. is it safe to power the s5 with just 1 connector per blade?
Yeah, just make sure you use the ones nearest the ethernet port

So they are like the S3's? No need for all 4 connections unless you'll overclock? Didn't know that.
It's not recommended, but I run a couple like that without issues - never tried OCing them though, wouldn't risk it tbh

Edit: Good quality gauge wires are essential though.
thanks! i assume they recommend connecting all 4 is to prevent the wires from getting too hot and the connectors on the blade are in parallel