I picked up my Portable's original white power adapter (7.5V 1.5A) on ebay for $45 shipped, earlier this year. They come up fairly often, though not regularly, on eBay. I find Portable stuff at decent prices to be more of a waiting game than anything.
If you have a 5126 (backlit version), the powerbook 2.0a adapter will work. The 5126 actually has the input power rating at 2.0a, not the 1.5a of the 5120 adapter. I have had no ill effects using the lower rated adapter, though. I don't know how long it should take to fully charge the portable's main battery, but I would assume it's between 2-3 hours. I just leave mine plugged in overnight before doing anything with it.
If you have a 5126 (backlit version), the powerbook 2.0a adapter will work. The 5126 actually has the input power rating at 2.0a, not the 1.5a of the 5120 adapter. I have had no ill effects using the lower rated adapter, though. I don't know how long it should take to fully charge the portable's main battery, but I would assume it's between 2-3 hours. I just leave mine plugged in overnight before doing anything with it.