Self-powered USB hub and power supply adapter ampere capacity

I am looking for a power supply adapter for my USB Hub so it can support at least 2 bus-powered external hard drives. The hub's rating is 5 volts, 2 amperes. I would like to know if it would be OK to buy a power supply adapter rated at less than 2A. I've been looking for power supply adapters and the ones that do support 2A are more expensive (more expensive than the USB hub itself) compared to those that support less than 2A. Will a power supply adapter that supports less than 2A (~1-1.5A) work fine to support two external hard drives? The external hard drives are both bus-powered Western Digital My Passport Essentials 250 GB. The OS is Windows XP SP3.

There are 2 possible answers here, but one carries risk, the text book answer is NO, the people that made that unit are the experts, so if that is what they determined to be the spec of that unit, then that is what it must be. That said many people use adaptors that are of a lesser spec and have got lucky, but I certainly would NOT take the chance personally, it's one thing to take a chance on cheap gadgets that if worst case you wouldn't worry about binning them, but if something has value I would not take the chance, not unless someone qualified in electrics was able to say for sure what would happen, so unless you find someone in this sort of area I would not risk it personally. All that said I have a powered hub here, and because I'm doing the front room up I'm stripped down to bare essentials, and the hub is running without any power attached at this time, I don't know what the ramifications of this are, maybe if something needs some power it would not be able to manage, but I attach my mobile phone, thumb drive etc without issue, and without power, and they work OK, see if you can do this, but ultimately your safest and probably cheapest option is to get another hub, I'd of thought there are cheap ones around, sorry I couldn't offer more help than this.