You need citations for Congressional use of the "power of the purse"? Really?
Here in the United States, the term Power of the Purse refers to relationship between Legislative and Executive branches of the same government.
The relationship discussed in this sub-thread is between different governments: Federal vs. local ones...
Because communities are often not as in charge of their police departments as they should be or think they are
In other words, you do think, Washington "knows better" than the local doofuses . Right... Why, I wonder, even bother with elections there — instead of letting the sophisticated Washingtonian nobility appoint one of their own...
Where's the injustice here?
Your granpa can demand you do something in exchange for his contribution to your pocket money — that's Ok, because it is his money... On contrast, the monies the Feds disburse as subsidies are not theirs to attach strings to. They use this method to get around the 10th Amendment — and I consider it unjust.
Congress has the power of the purse.
Only over President... This was, indeed, part of the "checks-and-balances" from day one. Congress was never supposed to have the same power over States and towns however. And — contrary to your earlier assertion — did not have it, until Federal taxes grew up so much...