Let
![$x\geq1$](img2.png)
be a real number and
![$T_{n}(m)=-1^{m}+2^{m}-\cdots+(-1)^{n}n^{m}$](img3.png)
, where
![$n$](img4.png)
and
![$m$](img5.png)
are nonnegative integers with
![$n\geq1$](img6.png)
. In this note we obtain an explicit formula for
![$T_{\lfloor x\rfloor}(m)$](img7.png)
, where
![$\lfloor x\rfloor$](img8.png)
is the greatest integer less than or equal to
![$x$](img9.png)
, and we establish a new expression for alternating power sums
![$T_{n}(m)$](img10.png)
in terms of Stirling numbers of the second kind. Moreover, we give a congruence involving alternating sums of falling factorial.