The supernova G2, P2, T2, and B2 are all made by Super Flower (very very good).
The supernova GS and PS are all made by Seasonic (also very very good).
The rest are made by an assortment of manufacturers, FSP, HEC, Etasis, and some others (bad to mediocre).
Of these, the G2, P2, and T2 are the best.