It is underpowered because the 1060 needs a minimum of a 400W PSU. You then have to take into account the efficiency of the PSU into account, again, and it can offer on a consistent basis 280W. Take a look at the sticker on the side of the PSU. You could also take a pic. Do you see +12V? What's the number(s) directly below that. It should say something like 35A but it's probably closer to 20. That +12V rail i what feeds the GFX card.
If you want to know what your components would draw from the wall....look at the specs of each component....add up the power draws and divide by the efficiency.
If the efficiency is 80%......divide by .8. 90%....divide by .9 and so on.
I've seen it so many times where people compute the draw, and then just *.8, or *.85