The WM050 series of power supplies are all completely sealed (glued shut) The output current is on the low side for used with a wireless SB when the display is on full brightness.
The WM075 series has a higher current capability and has three screws in the case. The WM220 series use a much larger transformer and is rated at 2 amps. I would not suggest the WM050 series. I really do not think it can provide enough current to use with the SB safely.
The WM075 is the least expensive ELPAC I would suggest. The WM220, either stock of modded, sounds a lot better than the wall wart WM075.
You can sometime find the WM220 surplus on E-bay. There is currently one available now
hereI do not know this seller. I have modded many an ELPAC sent to me from sellers on E-Bay. They have all been able to ship the product direct to me for modding. For $35.00 for the power supply including shipping, this looks like a good deal.
I charge $125.00 for the mod plus about $10.00 for shipping $170.00 for a modded PS shipped to your home is a pretty good deal.