nearby power is 230vac
Pure guess - you are in continental USA? Now how many times have I tried to persuade EVERY correspondent to edit their profile to show at least their continent/preferably nation - it helps to help!
All domestic properties in USA (probably Canada & Mexico) are served by a 220/230/250Vac supply which runs their appliances (washer, dryer, fridge, cooker) as is. The line is split to (at least two) 110Vac to supply domestic sockets and lighting. Most of RoW on 110Vac do something similar.
Normally, PSUs supplied in the Americas are supplied with 110Vac set, but many will have the little black slotted switch on the rear to change to 220/230Vac - FLIP THIS. If it isn't fitted (there will be a small oblong cut-out blanked off), the option usually exists inside the box because all PSUs are created equal in which case a couple of extra wires may be needed. [Very, very early units may have been made in the US and omit the extra components to save cost, but I haven't had the opportunity to check this.]
BUT IF YOU ARE UNCOMFORTABLE OPENING THE BOX WHICH IS ALWAYS LABELLED 'DANGER' OR 'HAZARD' - GET SOMEONE ELSE TO DO THE CONVERSION BECAUSE dc CAN KILL - IT ONLY GOES ONE WAY(!) SO LOCKS UP YOUR MUSCLES. YOUR HEART IS A MUSCLE, TOO. But don't go overboard - I've made a hobby of fixing dead PSUs and the guys who make them test them by the thousand every day before the lids go on.
After that, you need to find one red and one black lead going to a 4-socket Molex (just a name) floppy/hard disc/CD-DVD connector. There are usually at least two of these even on old AT boxes. Snip one each cable at the connector end. No need for soldering anything, just force the red one onto the GPIO pin 2 (look it up if you don't know the numbering system which is "opposed" ie 2 is
opposite 1 and 4, 6,8, etc are
next to each other on the same side)), force the black one onto pin 6. That provides your power. If it's an AT PSU just plug in and switch on once you have the correct ac line voltage set. For an ATX supply, use a short length of insulated copper wire, ends trimmed, to push in and short the green ( orange, blue, black GREEN etc, etc down one side) and black sockets on your 20(/24) motherboard power lead, then just plug ac cord into wall socket.
There is no more to say. If you cannot follow those steps, there's probably plenty of folks who'll help; once shown, never forgotten. Above is written for complete neophytes so please don't be offended if you, dear reader, are a designer/repairman of electronic/electric equipment.
Either way, be sure to report back success for the benefit of anyone else unsure.
Anecdotal: Why 230Vac? Why 110Vac? Leaving aside the great debate about ac vs. dc., the US was originally persuaded that 110Vac was 'safer' than 250Vac. It turned out to be nonsense. On the one hand, very few fit healthy folk are killed by 250Vac - they die when they are thrown backwards and crack their scull on the Out house sink! Neither is 110Vac any 'safer' from consequential disaster. Maybe some value <90Vac might be less 'shocking', at least for some individuals. The downside of using 110Vac is the need for thicker and much more expensive copper wiring, apart from the greater problem of iR losses, lower reliability against minor defects normally encountered during the lifetime of products, etc. In practice, the selection of 220/230/240Vac has proved a wise choice leading to lower costs and higher reliability. The bizarre effect in the USA, in particular, is, as indicated above, virtually all buildings possess a 250Vac supply; virtually all could change over to 250Vac outlets and lighting at modest cost and significant savings in the longer term. Could there be an element of arrogance not to do that?!