I have an electrical equipment(Its quite old. aybe about 25 years old)These are the ratings:Input : AC 120 V 60 HzOutput : DC9V - 850mAI live in SIngapore which has a power input of 240VMy step down transformer/converter specsMaximum power it can convert is 230 watts
DC9V @ 850mA is 7.65 watts. Your stepdown transformer can handle 230 watts so a measly 7.65 watts is no problem for it. Use it with confidence. Or buy a replacement AC adapter with an input of 240vAC, output of 9vDC for a lot cheaper. As long as the adapter output is rated for 850mA or higher, it will be good. (Make sure the polarity is correct, as well as the physical fit of the coaxial connector.)
Your existing transformer/converter will work just fine. Even if it's only 25% efficient your adapter will be pulling just 36 watts. Your transformer is good for over six times that. So you're ok. You want the transformer to have a capacity of at least 20% over the actual load, but more capacity is perfectly ok. Of course, you could also replace your power adapter with one that takes 240V input. That would be a lot more convenient. In the US such adapters normally cost less than 10 USD.
