PSU quality is not about brand. It's about specific models.

Since there is no "we only sell good rock-solid product" brand on the market,
most of product from "good brand" are cheap, low-end, or worse, expensive and high rated output with bad performance characteristics.

I don't know anything about the compatibility issues with avalon asic, so i cannot say anything about it.
However, this is a list of top notch 800W+ output PSU you can find on the market today.

Seasonic P-860 SS-860XP2 (in-house)
Seasonic P-1000 SS-1000XP (in-house)
Corsair AX860 (Seasonic OEM)
Corsair AX860i (Flextronics OEM)
Corsair AX1200i (Flextronics OEM)

And belows are slightly worse PSU compared to above.

SuperFlower Golden King 850W SF-850P14PE (in-house)
SuperFlower Golden King 1000W SF-1000P14PE (in-house)
Fractal Design Newton R3 800W FD-PSU-NT3B-800W (ATNG OEM)
Fractal Design Newton R3 1000W FD-PSU-NT3B-1000W (ATNG OEM)

Anything other than listed is typically worse including Enermax Platimax/MAXREVO, Antec HCP, Corsair CX, CoolerMaster SPH, SuperFlower Golden Green, Zalman Platinum, FSP Aurum Pro and so on though they are not in the same ground. actually, a few of them has matching characteristics with above listed. In this case, they're not listed because they're 80 plus gold PSU.

Anyway, Avalon's original PSU is 2 BTC worth. It means original PSU cannot be good one considering exchange rate of pre-order period. Their originally equipped PSU must be worse than Enermax Platimax/MAXREVO, Antec HCP, Corsair CX, CoolerMaster SPH, SuperFlower Golden Green, Zalman Platinum, FSP Aurum Pro.

Avalon homepage stated that the power consumption is "~ 600w @ 120v AC". Therefore, the data probably came from wall power meter like kill-a-watt. and less than 600W wall draw with cheap power probably means 450watt-ish real power consumption, so 4 module one's actual power consumption would be around 600watt, at best 700w. In other words, Good 600-650W PSU probably won't blow up with 4 module Avalon since high quality PSU typically can handle 110-120% load for a considerably long time.

However, long term exposure of near 100% or above 100% load is definitely not a good thing for PSU even if it's a good one, so I would recommend 800W+ good PSU. And maximum efficiency typically achived within 40-60% load range of PSU, Corsair AX1200i looks fine if there is no size issue(AX1200i is slightly longer than typical ATX PSU).