Ok so your Qty will be -190 in this case the Cost will auto populate with what the cost is on the item (average cost of the item).
If average cost is zero Unit Cost is zero then 190 will be taken out of stock and there will be no GL impact as 190*0 is 0.
If they have an average cost for example of $1 then they are valued at $190 in stock so when you do adjustment the GL will credit 190 out of stock and debit the stock adjustment with 190. If you change the Unit Cost on the line it wont matter it will still take them out of stock at $1 as it cannot leave a value in inventory for them item if there is no stock qty.
Hope this makes sense.