Can I use home appliances from Singapore in Thailand w/o and adaptors? 

Same power, but you'll need to either change the plug, or use an adapter so it will fit most Thai style sockets:

 

What I do is use locally bought power strips with universal sockets.  The two round pins on the plug fit Thai style outlets:

7 hours ago, ballpoint said:

The two round pins on the plug fit Thai style outlets:

 

They do.

 

BUT!!

 

That Shuko plug will leave your strip with no ground. Of course if you only use Class-2 (double insulated) appliances all will be fine but any Class-1 appliances will be potentially lethal. Best to put a proper 3-pin plug on the end.

 

And yes, Singapore appliances will work just fine here.