Add ability to detect power supply source on Windows.

Duplicati/Library/Utility/Duplicati.Library.Utility.csproj

@@ -43,6 +43,7 @@
     <Reference Include="FasterHashing">
       <HintPath>..\..\..\packages\FasterHashing.1.2.1\lib\net45\FasterHashing.dll</HintPath>
     </Reference>
+    <Reference Include="System.Windows.Forms" />
   </ItemGroup>
   <ItemGroup>
     <Compile Include="AsyncHttpRequest.cs" />
@@ -80,6 +81,7 @@
     <Compile Include="Power\IPowerSupplyState.cs" />
     <Compile Include="Power\DefaultPowerSupplyState.cs" />
     <Compile Include="Power\LinuxPowerSupplyState.cs" />
+    <Compile Include="Power\WindowsPowerSupplyState.cs" />
   </ItemGroup>
   <ItemGroup>
     <None Include="app.config" />

Duplicati/Library/Utility/Power/PowerSupply.cs

@@ -39,6 +39,10 @@ namespace Duplicati.Library.Utility.Power
             {
                 state = new LinuxPowerSupplyState();
             }
+            else if (Utility.IsClientWindows)
+            {
+                state = new WindowsPowerSupplyState();
+            }
             else
             {
                 state = new DefaultPowerSupplyState();

Duplicati/Library/Utility/Power/WindowsPowerSupplyState.cs

@@ -0,0 +1,46 @@
+//  Copyright (C) 2017, The Duplicati Team
+//  http://www.duplicati.com, info@duplicati.com
+//
+//  This library is free software; you can redistribute it and/or modify
+//  it under the terms of the GNU Lesser General Public License as
+//  published by the Free Software Foundation; either version 2.1 of the
+//  License, or (at your option) any later version.
+//
+//  This library is distributed in the hope that it will be useful, but
+//  WITHOUT ANY WARRANTY; without even the implied warranty of
+//  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+//  Lesser General Public License for more details.
+//
+//  You should have received a copy of the GNU Lesser General Public
+//  License along with this library; if not, write to the Free Software
+//  Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
+
+using System.Windows.Forms;
+
+namespace Duplicati.Library.Utility.Power
+{
+    public class WindowsPowerSupplyState : IPowerSupplyState
+    {
+        public PowerSupply.Source GetSource()
+        {
+            try
+            {
+                PowerLineStatus status = System.Windows.Forms.SystemInformation.PowerStatus.PowerLineStatus;
+                if (status == PowerLineStatus.Online)
+                {
+                    return PowerSupply.Source.AC;
+                }
+                if (status == PowerLineStatus.Offline)
+                {
+                    return PowerSupply.Source.Battery;
+                }
+
+                return PowerSupply.Source.Unknown;
+            }
+            catch
+            {
+                return PowerSupply.Source.Unknown;
+            }
+        }
+    }
+}