What I was thinking, a simple zero cross snubberless SSR relay in there, nothing more. Wonder what the leakage current of the switch is, those can be a big nuisance with small loads that will either never actually be turned off ( thus negating any power savings) or worse that sit in a voltage level that will either cause a brownout or regular malfunctions that seemingly are random, to totally blowing up the supply as it tries to regulate the switch on time past 100%.
Then also wonder just what they are using as a power supply, and how much it also uses, and how well protected it is as well.
Joe, just for a lark, can you put a few USB wall warts ( not the cheap ones, but ones from reputable manufacturers, because we all know how the cheap ones will fail anyhow) across your line simulator and see what it takes to kill them. My guess is that almost all of them will fail 2kV, but just how badly they do this, and how much they smoke doing so. Most will probably work fine with your test voltage, being universal input devices. You will just need a sacrificial USB voltage monitor and a resistor to draw 100mA to 500mA out of them during the test. Pretty much how they behave in transient conditions, and what a simple mains transient like a motor disconnect on the same branch circuit will affect them.