Ho seh... though I don't really know much about Acer PC, those
sliders are for adjusting voltages. By adjusting with the power
turn on, you are asking for trouble. Thank goodness only smoke came
out, or you could see yourself in hospital.
Reading your description, I can guarantee that at least your PSU is
gone case, since the slider is on the PSU. There's also a chance
that your whole CPU might be gone, so you need to purchase a brand
new one. Luckily SITEX is until Sunday... 
Thanks for boosting Singapore's economy.
If your warranty is not over, you have to bring over to Acer
Service Centre at Jurong. Just lie to them that there is a power
outrage and it becomes like that. And slide back the red slider to
its original position if not you have to pay a great deal. If
warranty is over, just bring it to your nearest PC shop. Depending
on how severe the damage is, you have to pay anything from $30 to
$300.
