PSU question

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Hi i have just purchased a PSU & it is a 170w that i think was designed for the 520 with dock.
Its the same standard connector as most of my thinkpads
Is this worth keeping for the future & is it ok to use with my older machines & docks.
My other PSUs are only 65w & 90w i think.
Just wondering if there are any advantages or disadvantages to using this?
eg: good perhaps more headroom so may last longer?
Bad takes more power so higher running costs?
Any thoughts?
Thanks