Maybe instead of changing out the connector, a source of wall warts could be found that have a Type-A jack?
Like those that come with the iPhone and iPod Touch? I here there are a few of those around...
dealextreme has them, rated at 1000mA even, for around US$3.
Type B seems to me to have a "more positive" (less negative?) attachment than the mini connectors.
I've had enough problems with friction-fit cables that I want a positive latch on every connection - screws (ala DB9) or some other latch (like the RJ series tabs).
-j