Can you use fusion blades with the fusion power razor?

Yes. below is copied and pasted from Gillettte's website.

Answer A number of our razors are based on the multiple blade concept. Although we realize that the cartridges may be somewhat similar in appearance, the shaving systems themselves are quite different and cartridges are not interchangeable. For this reason, we make sure that our packaging clearly states the name of the razor and cartridges that are designed to fit that razor.

For your convenience, here's a compatibility list:
• All Fusion family Razors and Cartridges are interchangeable.
• All MACH3 family Razors and Cartridges are interchangeable.
• All Sensor Family Razors and Cartridges are interchangeable.
• TRACII Plus works with TracII or TracII Plus Cartridges
• Atra Plus Razor works with Atra or Atra Plus Cartridges.
• Contour Razor works with Contour Plus cartridges.