STROBE SHOOTOUT: S&S
YS90DX, INON Z220, INON D180

YS90DX (left side) vs Z220 @ 1/500s shutter, diffuser off, both at full
power

YS90DX vs Z220 @ 1/1000s shutter, diffuser off, both at full power

YS90DX vs Z200 @ 1/2000s shutter, diffuser off, both at full power

D180 (left side) vs Z220 @ 1/500s shutter, diffuser off, both at full
power

D180 (left side) vs Z220 @ 1/1000s shutter, diffuser off, both at full
power

D180 (left side) at full power vs Z200 at 1/2 power, @1/500s shutter,
diffuser off
It looks like the Z220 is much brighter than the YS90DX, but it
does so by staying on longer. At shutter speeds above 1/500s the
measured brightness of the Z220 starts to drop; the strobe light gets
cut off by the shutter. Even at 1/2000s the Z220 still looks a little
brighter than the YS90DX. The D180 behaves just like the Z220 but 1
stop dimmer. This is consistant with what Mark told me, that they are
the same except the Z220 have two capactors and the D180 only has one.

Here's a size comparison.