There are various external USB drives, some require external power supplies, some have optional external power supplies, some have 2 USB plugs, 1 for power and 1 for power + data. If I have a device with a single USB 2.0 port, is there any way to find out if a specific USB DVD reader will receive sufficient power through that port, other than manually testing the drive by plugging it in?

Based on existing answers, comments, and close votes, some people may not be familiar with the problem:
The maximum power delivered through USB ports varies by implementation. Not every USB2.0 port is the same. Many (or one be tempted to say "most") notebooks and tablets have underpowered USB ports. The same is true for USB 3 ports. Random example: <http://forum.tabletpcreview.com/threads/surface-pro-3-problem-with-external-dvd-drive.63207/>

> 
> But many of the Windows Tablets deliberately under-power the USB Port
>  to conserve the battery life, the SP3 happens to be one that does this
>  (SP2 as well)....not having the Power Connector is why I suggested the
>  "Y" cable, it ensures that the device gets the 5 volts needed to power
>  the device....
> 
> 
> 

Background: I'm looking for a pair of a 300-400$ "Atom" laptop/tablet and a DVD drive where the DVD drive has to be connected with a single cable (not 2 USB cables, no additional power cable). I don't care about writing DVD, or about any speed beyond "fast enough to play a movie".

The only working approach that I currently know of is to search the internet for customers using a specific device, who write how they already tried a couple drives that didn't work, and then finally found one model that worked. But I really hope there's a better approach.