This is a different inverter

Probably none of you would buy this 150W 12V inverter. What makes it interesting is it is listed as having 110V AC out. What it actually puts out is 140V DC. I've actually taken small inverters like this and modified them to put out DC when the H bridge failed. Wall warts and many other devices work fine on DC, are more efficient and don't produce hum in audio equipment. But these guys are just hoping nobody puts a transformer on one of these. I really like this model. It is very compact and at idle only draws 75ma, no fan needed. Even has a PD port. No ground pin and the negative side of the 140V is tied to battery neg.

How dangerous is 1A of DC arcing (either when disconnecting or within switchgear/fuses) at 140V?

Is it designed to put out 140 vdc? Or has it failed/been modified to put out straight DC?

It was designed to put out DC and I think the seller has removed all the instructions so nobody finds out till it is too late. The normal neutral pin is the one at 140V DC. Usually, the hot has the switch in consumer powered devices. The neutral being powered leaves these devices mostly electrically hot in the off state. I think the market will be flooded with these inverters. I usually suggest these small 150W inverters for pond aerators that have 60W pumps. DC will burn these out.