Sim Lim tower is actually better for maker stuff than Sim Lim square. The two are just across the street from each other.
(I hope I'm not mixing them up.)
(I hope I'm not mixing them up.)
But in Singapore, the mother lode is probably Koba Electronics[1] in Chinatown..
[1] http://dangerousprototypes.com/2012/08/06/global-geek-tour-s...
Around the Sim Lims (and across the island) you also have lots of small hardware shops.