One thing that I discovered about charging PS3 pads, which doesn't seem to be mentioned a lot, is that they appear (my guess, unconfirmed) to require proper USB current negotiation before they will start charging. In fact, I've found multiple sources saying that they can be charged from any USB power source, which isn't true.

The original USB standard states that USB hosts should start a connection with 100mA of current, and the client can request increases in 100mA steps up to 500mA. I assume that the PS3 USB ports support this, as do pretty much all computer USB ports. But the majority of wall plug USB chargers don't; they just allow a maximum current draw of 500mA (or more) from the start and ignore increase requests.

It seems like the majority of equipment manufacturers ignored this part of the spec, since the host needs circuitry to limit current in any case, so many chargers don't bother with circuitry to respond, and even when the port does respond to increase requests, the port is actually always allowing the maximum draw and simply approving all requests.

However, I think that the PS3 pads actually wait for an "OK" response before continuing, which the majority of wall chargers (especially the cheap ones) never send. I had to use the PS3 or a PC (direct connection, not through a hub) to charge my pads until I found a cheap PS3 controller charging dock that works with any supply.