The choice is yours. I'd have gone for the voltage transformer! But you're right that there is a risk factor, however small.

You probably don't have a motherboard manual, so it might be a good idea to take a photo of your mobo with the power leads clealry shown because you need to correctly reassign these from the new PSU.

You could then dismantle the PSU and take it to the shop for double assurance.

What about the screen. Are you sorted there?