diff --git a/OpenRA.Game/Traits/Player/PowerManager.cs b/OpenRA.Game/Traits/Player/PowerManager.cs
index e3bc100476..0eaf4a5398 100644
--- a/OpenRA.Game/Traits/Player/PowerManager.cs
+++ b/OpenRA.Game/Traits/Player/PowerManager.cs
@@ -102,11 +102,13 @@ namespace OpenRA.Traits
 			}
 		}
 		
-		public PowerState GetPowerState()
+		public PowerState PowerState
 		{
-			if (PowerProvided >= PowerDrained) return PowerState.Normal;
-			if (PowerProvided > PowerDrained / 2) return PowerState.Low;
-			return PowerState.Critical;
+			get {
+				if (PowerProvided >= PowerDrained) return PowerState.Normal;
+				if (PowerProvided > PowerDrained / 2) return PowerState.Low;
+				return PowerState.Critical;
+			}
 		}
 	}
 }
diff --git a/OpenRA.Game/Traits/Player/ProductionQueue.cs b/OpenRA.Game/Traits/Player/ProductionQueue.cs
index 570268e1bc..9c6906688b 100644
--- a/OpenRA.Game/Traits/Player/ProductionQueue.cs
+++ b/OpenRA.Game/Traits/Player/ProductionQueue.cs
@@ -276,7 +276,7 @@ namespace OpenRA.Traits
 
 			if (Paused) return;
 
-			if (pm.GetPowerState() != PowerState.Normal)
+			if (pm.PowerState != PowerState.Normal)
 			{
 				if (--slowdown <= 0)
 					slowdown = Queue.Info.LowPowerSlowdown; 
diff --git a/OpenRA.Game/Traits/Player/TechTree.cs b/OpenRA.Game/Traits/Player/TechTree.cs
index f2c9b9e3ca..5a5af226ca 100755
--- a/OpenRA.Game/Traits/Player/TechTree.cs
+++ b/OpenRA.Game/Traits/Player/TechTree.cs
@@ -14,12 +14,12 @@ using OpenRA.FileFormats;
 
 namespace OpenRA.Traits
 {
-	class TechTreeInfo : ITraitInfo
+	public class TechTreeInfo : ITraitInfo
 	{
 		public object Create(ActorInitializer init) { return new TechTree(init);}
 	}
 
-	class TechTree
+	public class TechTree
 	{
 		readonly List<Watcher> watchers = new List<Watcher>();
 		readonly Player player;
@@ -42,10 +42,16 @@ namespace OpenRA.Traits
 			foreach(var w in watchers)
 				w.Update(buildings);
 		}
-
+		
 		public void Add(string key, List<string> prerequisites, ITechTreeElement tte)
 		{
-			watchers.Add(new Watcher( key, prerequisites, tte ));
+			Add(key, prerequisites, false, tte);
+		}
+		
+		// set requiresPowered = true to discard buildings that have an IDisabled active (eg manually powered down)
+		public void Add(string key, List<string> prerequisites, bool requiresPowered, ITechTreeElement tte)
+		{
+			watchers.Add(new Watcher( key, prerequisites, requiresPowered, tte ));
 		}
 
 		public void Remove(string key)
@@ -53,7 +59,7 @@ namespace OpenRA.Traits
 			watchers.RemoveAll(x => x.key == key);
 		}
 		
-		public static Cache<string, List<Actor>> GatherBuildings( Player player )
+		static Cache<string, List<Actor>> GatherBuildings( Player player )
 		{
 			var ret = new Cache<string, List<Actor>>( x => new List<Actor>() );
 			if (player == null)
@@ -77,25 +83,28 @@ namespace OpenRA.Traits
 			public readonly List<string> prerequisites;
 			public readonly ITechTreeElement watcher;
 			bool hasPrerequisites;
-
-			public Watcher(string key, List<string> prerequisites, ITechTreeElement watcher)
+			bool requiresPowered;
+			
+			public Watcher(string key, List<string> prerequisites, bool requiresPowered, ITechTreeElement watcher)
 			{
 				this.key = key;
 				this.prerequisites = prerequisites;
 				this.watcher = watcher;
 				this.hasPrerequisites = false;
+				this.requiresPowered = requiresPowered;
 			}
 
 			public void Update(Cache<string, List<Actor>> buildings)
-			{
+			{                   
 				var nowHasPrerequisites = true;
 				foreach (var p in prerequisites)
-					if (!buildings.Keys.Contains(p))
+					if (!buildings.Keys.Contains(p) || 
+					    (requiresPowered && buildings[p].All(b => b.TraitsImplementing<IDisable>().Any(d => d.Disabled))))
 					{
 						nowHasPrerequisites = false;
 						break;
 					}
-								
+				
 				if( nowHasPrerequisites && !hasPrerequisites )
 					watcher.PrerequisitesAvailable(key);
 
@@ -107,7 +116,7 @@ namespace OpenRA.Traits
 		}
 	}
 
-	interface ITechTreeElement
+	public interface ITechTreeElement
 	{
 		void PrerequisitesAvailable(string key);
 		void PrerequisitesUnavailable(string key);
diff --git a/OpenRA.Game/Traits/SupportPower.cs b/OpenRA.Game/Traits/SupportPower.cs
index a886d434f8..f99dc1a6d4 100644
--- a/OpenRA.Game/Traits/SupportPower.cs
+++ b/OpenRA.Game/Traits/SupportPower.cs
@@ -47,7 +47,6 @@ namespace OpenRA.Traits
 
 		protected readonly Actor Self;
 		protected readonly Player Owner;
-		string[] effectivePrereq = {};
 		
 		bool notifiedCharging;
 		bool notifiedReady;
@@ -60,9 +59,6 @@ namespace OpenRA.Traits
 			Self = self;
 			Owner = self.Owner;
 			PlayerPower = self.Trait<PowerManager>();
-
-			effectivePrereq = Info.Prerequisites
-				.Select(a => a.ToLowerInvariant()).ToArray();
 			
 			self.Trait<TechTree>().Add( Info.OrderName, Info.Prerequisites.Select( a => a.ToLowerInvariant() ).ToList(), this );
 		}
@@ -74,8 +70,8 @@ namespace OpenRA.Traits
 			
 			if (Info.GivenAuto)
 				IsAvailable = hasPrerequisites;
-							
-			if (IsAvailable && (!Info.RequiresPower || IsPowered()))
+
+			if (IsAvailable && (!Info.RequiresPower || PlayerPower.PowerState == PowerState.Normal))
 			{
 				if (Game.LobbyInfo.GlobalSettings.AllowCheats && self.Trait<DeveloperMode>().FastCharge) RemainingTime = 0;
 
@@ -97,16 +93,6 @@ namespace OpenRA.Traits
 			}
 		}
 
-		bool IsPowered()
-		{
-			if (effectivePrereq.Count() == 0) 
-				return PlayerPower.GetPowerState() == PowerState.Normal;
-			
-			// Takes 0.3ms on pchote's machine -- calling it every tick for every active special power is retarded
-			var buildings = TechTree.GatherBuildings(Owner);
-			return effectivePrereq.All(a => buildings[a].Any(b => !b.TraitsImplementing<IDisable>().All(d => d.Disabled)));
-		}
-
 		public void FinishActivate()
 		{
 			if (Info.OneShot)
@@ -135,7 +121,7 @@ namespace OpenRA.Traits
 			if (!IsAvailable || !IsReady)
 				return;
 
-			if (Info.RequiresPower && !IsPowered())
+			if (Info.RequiresPower && PlayerPower.PowerState != PowerState.Normal)
 			{
 				var eva = Owner.World.WorldActor.Info.Traits.Get<EvaAlertsInfo>();
 				Sound.Play(eva.AbilityInsufficientPower);
diff --git a/OpenRA.Mods.RA/CanPowerDown.cs b/OpenRA.Mods.RA/CanPowerDown.cs
index f6c0049929..012491a7bc 100755
--- a/OpenRA.Mods.RA/CanPowerDown.cs
+++ b/OpenRA.Mods.RA/CanPowerDown.cs
@@ -22,11 +22,13 @@ namespace OpenRA.Mods.RA
 		[Sync]
 		bool disabled = false;
 		int normalPower = 0;
-		readonly PowerManager PlayerPower;
+		readonly PowerManager PowerManager;
+		readonly TechTree TechTree;
 		
 		public CanPowerDown(ActorInitializer init)
 		{
-			PlayerPower = init.self.Owner.PlayerActor.Trait<PowerManager>();
+			PowerManager = init.self.Owner.PlayerActor.Trait<PowerManager>();
+			TechTree = init.self.Owner.PlayerActor.Trait<TechTree>();
 			normalPower = init.self.Info.Traits.Get<BuildingInfo>().Power;
 		}
 		public bool Disabled { get { return disabled; } }
@@ -39,7 +41,10 @@ namespace OpenRA.Mods.RA
 				var eva = self.World.WorldActor.Info.Traits.Get<EvaAlertsInfo>();
 				Sound.PlayToPlayer(self.Owner, disabled ? eva.EnablePower : eva.DisablePower);
 				
-				PlayerPower.UpdateActor(self, disabled ? 0 : normalPower);
+				PowerManager.UpdateActor(self, disabled ? 0 : normalPower);
+				
+				// Rebuild the tech tree; some support powers require active buildings
+				TechTree.Update();
 			}
 		}
 	}
diff --git a/OpenRA.Mods.RA/HackyAI.cs b/OpenRA.Mods.RA/HackyAI.cs
index 5904631a43..16e1c89679 100644
--- a/OpenRA.Mods.RA/HackyAI.cs
+++ b/OpenRA.Mods.RA/HackyAI.cs
@@ -31,7 +31,6 @@ namespace OpenRA.Mods.RA
 		bool enabled;
 		int ticks;
 		Player p;
-		PlayerResources playerResources;
 		PowerManager playerPower;
 		
 		int2 baseCenter;
@@ -70,8 +69,6 @@ namespace OpenRA.Mods.RA
 		{
 			this.p = p;
 			enabled = true;
-		
-			playerResources = p.PlayerActor.Trait<PlayerResources>();
 			playerPower = p.PlayerActor.Trait<PowerManager>();
 		}
 
diff --git a/OpenRA.Mods.RA/OreRefinery.cs b/OpenRA.Mods.RA/OreRefinery.cs
index 3ca05b4168..8760db3b43 100644
--- a/OpenRA.Mods.RA/OreRefinery.cs
+++ b/OpenRA.Mods.RA/OreRefinery.cs
@@ -90,7 +90,7 @@ namespace OpenRA.Mods.RA
 					Ore -= amount;
 					PlayerResources.GiveOre (amount);
 				}
-				nextProcessTime = (PlayerPower.GetPowerState() == PowerState.Normal)? 
+				nextProcessTime = (PlayerPower.PowerState == PowerState.Normal)? 
 					Info.ProcessTick : Info.LowPowerProcessTick ;
 			}
 		}
diff --git a/OpenRA.Mods.RA/RequiresPower.cs b/OpenRA.Mods.RA/RequiresPower.cs
index 7f22060571..5a3f8c0f35 100644
--- a/OpenRA.Mods.RA/RequiresPower.cs
+++ b/OpenRA.Mods.RA/RequiresPower.cs
@@ -19,11 +19,9 @@ namespace OpenRA.Mods.RA
 
 	class RequiresPower : IDisable
 	{
-		readonly Actor self;
 		readonly PowerManager power;
 		public RequiresPower( Actor self )
 		{
-			this.self = self;
 			power = self.Owner.PlayerActor.Trait<PowerManager>();
 		}
 
diff --git a/OpenRA.Mods.RA/Widgets/BuildPaletteWidget.cs b/OpenRA.Mods.RA/Widgets/BuildPaletteWidget.cs
index 119e090204..4c58b6270d 100755
--- a/OpenRA.Mods.RA/Widgets/BuildPaletteWidget.cs
+++ b/OpenRA.Mods.RA/Widgets/BuildPaletteWidget.cs
@@ -454,7 +454,7 @@ namespace OpenRA.Mods.RA.Widgets
 			DrawRightAligned("${0}".F(cost), pos + new int2(-5, 5),
 				(resources.DisplayCash + resources.DisplayOre >= cost ? Color.White : Color.Red ));
 			
-			var lowpower = power.GetPowerState() != PowerState.Normal;
+			var lowpower = power.PowerState != PowerState.Normal;
 			var time = CurrentQueue.GetBuildTime(info.Name) 
 				* ((lowpower)? CurrentQueue.Info.LowPowerSlowdown : 1);
 			DrawRightAligned(WorldUtils.FormatTime(time), pos + new int2(-5, 35), lowpower ? Color.Red: Color.White);
diff --git a/OpenRA.Mods.RA/Widgets/PowerBinWidget.cs b/OpenRA.Mods.RA/Widgets/PowerBinWidget.cs
index ea62964c7e..03981f21a4 100755
--- a/OpenRA.Mods.RA/Widgets/PowerBinWidget.cs
+++ b/OpenRA.Mods.RA/Widgets/PowerBinWidget.cs
@@ -50,9 +50,9 @@ namespace OpenRA.Mods.RA.Widgets
 			float2 powerLevel = new float2(lastPowerProvidedPos.Value, barStart.Y);
 
 			var color = Color.LimeGreen;
-			if (power.GetPowerState() == PowerState.Low)
+			if (power.PowerState == PowerState.Low)
 				color = Color.Orange;
-			if (power.GetPowerState() == PowerState.Critical)
+			if (power.PowerState == PowerState.Critical)
 				color = Color.Red;
 
 			var colorDark = Graphics.Util.Lerp(0.25f, color, Color.Black);