Does buying a power supply from another country is not advisable?

The Corsair, like most computer power supplies, can accept AC input from 90 to 264 V, at 50 to 60 Hz. You might need to set some switches for this (but it should be automatic).

The AX860i is "Platinum Certified", which is better than gold. I could not find a "Gold" unit.

Is there an import duty for the Philippines?

First, I assume you are talking about a desktop computer ATX power supply. The words "power supply" could mean a lot of things nothing like a desktop computer power supply.
Assuming a desktop computer power supply, any new unit will either have a range switch or be fully auto-ranging, so the only thing you will need is the right power cord for the country that you are in. Note that small differences like 200VAC vs 240VAC are not important. If it has a switch, just pick 100 to 125 or 200 to 240VAC. 50/60 Hz does not matter and 400Hz(military) may also be supported since it makes almost no difference to a typical computer power supply. If by some miracle your power supply does not support the local voltage, replace it. A transformer would be a lot more expensive and other problems.

Contact the seller to supply 220V input model.

Should be good to go. Just need the right power cord.

E bay is just fine .Your probably getting a good deal that you have to wait a month to receive ..And it most of the tme get's there..One bad thing ...Saving all that money is hurting US economice .Good thing is we are deterring getting our As_es kicked by them

yup