USB To 3-Pin/4-Pin Cables
I found the cheapest USB to 3-pin and 4-pin fan cables on Shopee, at S$1.56 and S$1.41. I like that they include an on/off switch, much easier than re-plugging, handy for my spare Arctic P12 fan.
3-pin
3-pin plugs and travel adapters, including world-plug systems and socket keys.
Flip Duo World
After the Kickstarter success of the Flip British Plug, OneAdaptr announced the Flip World range in November 2017, spanning four products from the Duo to the Power World. Pre-orders got 30% off with the code WorldIn18.
Flip British Plug – Flip Quad
I backed the Flip British Plug on Kickstarter in November 2015, a project that raised £28,115 from 1,140 backers. I chose the £14 reward, paying about £19 with shipping for one Flip Quad, a thin, foldable British plug.
PowerPac Plug Key
I bought a packet of three PowerPac Plug Keys from Challenger at Funan for S$0.90, or S$0.72 with a 20% member's discount. Each Plug Key converts a 3-pin socket to accept a 2-pin power cable, since Singapore follows British standard.
Taiyo 3-Pin Plug Adapter
I bought a pack of two Taiyo 3-Pin Plug Adapters from Challenger at Funan for S$14.90, or S$13.41 with a 10% member's discount. I like that each of its three 3-pin sockets has an individual switch.