The main thing you look for the on an PSU is the 12V RAIL. In Picture above I red marked it for you. As more AMP you have on your Rail as more security / safty you build in that your PSU won't burn up and cause a potential fire.
So a GridSeed Blade only uses 100Watt maybe 120-140Watt if extreme overclocked. The other thing Jabberwork can also confirm is the AMP draw over those thinner ATX Cables cause heat on the Cable so as more you use in parallel as less heat you have on the cable. This is one reason why I highly recommend to go full on 14G-12G 120V Cable with solid copper core like shown in the picture. Those cables can take a BIG Load without producing the heat because they are solid copper. Also an very important factor which nobody tells you here is HEAT means you loose energy and efficiency. Not much but it ends up if you do run it like we do in Data Center settings.

So do your math :

12V and 100Watt  = 8.33 AMP

Yes you see it right one Gridseed Blade alone draws on DC Volt over 8 Amp. So we normally do have up to 4 units on 1 PSU so 32AMP is been drawn. And 70Amp can be handled. If you want to operate like a Data Center meaning 24h a day on your mining rigs than go this route so you don't burn down your house. Always leave 20-30% room on the 12V Rail otherwise you burn out those PSU's and you have to buy another one.