Non Thunderbolt Stock Chargers

I always thought all micro USB chargers were alike.
Like I thought this was going to be some kind of standard where as long as it plugs in, the phone will charge.

Last night I tried a different charger in my Thunderbolt.
(Not the stock charger that came with it).

My phone was completely dead (as it usually is by 9:00PM).
I first plugged in my son's droid charger; the original Verizon Droid with the slide out querty keyboard.
That didn't even get the light to start blinking on the Thunderbolt.
So then I plugged in my Kindle DX charger.
That got the light to come on.

Eight hours later I unplugged the Kindle charger from my ThunderBolt.
The phone had 40% charge, and I think that was wrong because it was dead again in 30 minutes.

I was going to buy a second charger on EBay, but now I am afraid that it won't have enough milliamp output to charge the battery.  I will just spend the extra bucks and get another charger from Verizon.

JedK

Are there specs somewhere?
What are the spec?

JedK