decrease in power upon acceleration on my volvo s60 2.5T

Has your check engine light come on? Have the system scanned for fault codes and post them on here to try and get an idea of what is going on? I believe you may be having an issue with the turbo control solenoid so your waste gate may not be opening up? The solenoid is located near the air cleaner housing. It will look like a little train with 3 color coded vacuum hoses. Red, yellow, and blue. Check that all hoses properly connected, check the turbo charge pipe and make sure that has not popped out. Down in the turbo there is a rubber hose that attaches the plastic pipe, Visually inspect that hose or just remove it to get a good visual and make sure that hose does not have a hole in it. Have seen a couple just go out like that? Inside the turbo make sure the turbine spins free and has no play. Using a small pressure pump, pump a couple of inches of pressure and make sure the waste gate does open up and is not binding up. If all that is good then the turbo control valve is bad. But verify first that it is a turbo issue by having the system scanned for fault codes. Keep me posted please.