I didn't notice it at the time I placed the order but my unit is different, and smaller capacity, than AkBKukU's.  Mine is Model PPWMB45 and claims to be designed for MacBook Air computers.  It has a different, but well made, enclosure and different specs but the same go-in-the-middle approach between the AC power cord and the MacBook adapter.  My unit claims 50.2 Wh storage on its faceplate but also claims a 10000 mAh/3.7 VDC battery which makes no sense (and the instructions claim 59.2 Wh storage!).  The instructions also claim an additional 4-5 hours of runtime for 13" and 11" MacBook Air computers respectively.  Strange.

There is a single-page set of instructions written in good English and with a reasonable amount of detail describing how to connect, charge and use the device.  The manufacturer is a company named Lenmar and at the date of this post their website brought up a "Under Construction" page with links for contact and warranty support.  They claim the device was designed in California and made in China.

Operation of the device is straight-forward.  It charges automatically when connected to AC power.  It supplies power to the Apple charger from battery only when disconnected from AC power and the power button is depressed for three seconds.  When connected to AC power it passes a version of that through directly while charging the batteries.  A set of 4 LEDs indicate charge status both when charging and discharging.  A green and red led around the power button indicate when it is powered or if it has detected a fault (over temperature for example).

I connected it to an old MacBook and it supplied power.  The MacBook was almost charged already and when the MagSafe connected LED turned green the ChugPlug turned off shortly after so I guess it powers off automatically when there is no load.

I connected my scope and then a DMM to the output.  This is where things start to get a little interesting.  On battery power it puts out 122 VDC.  On AC power it puts out 150 VDC (apparently derived from the US 120VAC mains).  Although strange it should be fine to feed a SMPS DC voltage since it will rectify the incoming AC immediately anyway.  Both voltages seem low however.  One might expect that a minimum DC voltage would be based on the Apple adapter's 100 VAC minimum input (1.414 x VACrms).  One would also expect that a rectified 120 VAC should be higher than 150 VDC.  I guess this is a good starting point for some reverse engineering...