Can I use a Thai iMac 24 power brick in the USA?

iMac - iMac Technical Specifications - Apple

sure their specs say

Electrical and Operating Requirements

• Line voltage:
• 100–240V AC

but unless thailand use the same ac plug as usa then you will need an adaptor

Thailand - Power Plugs & Sockets: Travel Adapter Needed?

US Thailand Travel Adapter 10A 250V (Type B), Convert Europe, UK, US, Australia To America Canada Japan Power Plug Converter 1500W Max, | Lazada

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thailand ac to us adapter - Google-

Hi,

Yes, you can, though you would need to get American standard AC cable or adapter.